Wednesday, 4 March 2015

Girls and boys in Sudan

At a time when I seemed a credible advisor on the topic, aspiring media psychologists used to ask me how to get on television. I replied that only two things were required: having an office near TV studios (my office at the Middlesex Hospital Medical School was in the middle of media land in central London) and having a popular subject, say the sexual fetishes of trauma victims who had been bitten by Royal dogs.

This blog is not a televisual event, but I hope to engage you with the popular and contentious subject of sex differences in intelligence. In part I am doing so because I intended to answer Nick Mackingtosh’s point that Richard Lynn’s work on sex differences had not been generally accepted. Sadly, Nick is no longer alive to participate, and the project was on the back burner anyway, because I thought it required going through many review papers and meta-analytic studies.

Now a paper comes along which gives a good introductory summary of the sex-differences-in-intelligence debate, and adds some new data on a large sample of over 7000 children. By way of background, all informed opinion was that men and women had the same level of intelligence, despite men’s 10% larger brain size. This paradox might have been resolved by showing that those extra neurones were required for the management of the penis. Not so, apparently. The proposal is that the extra capacity is taken up by greater visuo-spatial ability, which begs the question why it does not show up in intelligence measures. Richard Lynn upset the applecart by arguing that boys and girls matured at different rates, and when late maturing boys became men they were about 4-5 IQ points brighter than women. If one accepts that, plus the somewhat larger standard deviation for male intelligence (if one accepts that) then it is easy to see why there are more men at plus two sigma where all the interesting stuff happens. These larger issues to be discussed at a later time.

Salaheldin Farah Attallah Bakhiet, Bint-Wahab Muhammad Haseeb, Inas Fatehi Seddieg, Helen Cheng, and Richard Lynn (2015) Sex differences on Raven's Standard Progressive Matrices among 6 to 18 year olds in Sudan. Intelligence 50 (2015) 10–13.

They say: The Standard Progressive Matrices (SPM) was administered to a sample of 7226 school students aged 6 to 18 years in Sudan. The sample consisted of all the school students in the central sector of the provinces of Al Jazeera Aba, Raback, & Kosti in the White Nile state, approximately 300 km south of the capital, Khartoum. Schooling is compulsory in Sudan from the age of 6 and to 18 years.

The data were analysed for the sex differences on the total scores on the Standard Progressive Matrices and for the scores on the three factors of Gestalt Visualization, Verbal-analytic Reasoning and Visuo-spatial Ability identified by Lynn et al. (2004). To calculate scores on the three factors, a principal components analysis was carried out that showed three factors with eigenvalues greater than unity.

There were no statistically significant sex differences between the total scores of the 6 to 13 year olds, but among 14 to 18 year olds males obtained higher average scores than females and among the 16, 17 and 18 years olds the average male advantage was 0.337d, equivalent to 5 IQ points. An analysis of the data for the sex differences on the three factors of Gestalt Visualization, Verbal-analytic Reasoning and Visuospatial Ability identified by Lynn, Allik and Irwing (2004) showed similar age trends to those for the total scores.

 Table 1 gives the key findings:

image

If I had to talk about it on television I would show the picture below, with IQ on the ordinate. The sex differences are absolutely conclusive at age 17 but indifferent at age 18, and the graph makes that more clear than the table.

image

The picture makes the general pattern clear, with the switchover happening at age 11 when boys start to push ahead a bit, with more gains later. Even without the exceptional 17 year old performance, sex differences are evident.

The authors come to 4 conclusions:

1) no statistically significant sex differences for 6 to 13 year olds, suggesting girls are not disadvantaged in Sudan; (I could posit a later disadvantage)

2) there are sex differences later, broadly but not perfectly in line with Lynn’s 1994 predictions;

3) male advantage is visible at age 12 and statistically significant by age 14 in Sudan, sooner than predicted, and by 16 is at the equivalent of 5 IQ points;

4) the sex differences on the three sub-factors show similar although not identical age trends as those for the total scores. The only major difference is that on Visuo-spatial ability girls performed significantly better than boys at age 11 (.17d).

So, that ends the sex lesson. Lynn’s thesis about male advantage after age 16 was derived from data from European cultures. On any assessment of culture there are significant differences between growing up in Sudan and in Europe, but the same pattern is confirmed in this study. It seems more like sexual dimorphism than cultural constraints, though one can never be sure without comparing many different cultures, and this paper is one piece in the jigsaw.

One thing the paper did not do, because it was not the main topic, was to compare the overall levels of achievement with Western norms. If one takes age 15 as a comparison point then the average score of 28 in the Sudan would be below the 5th percentile on British or US norms. This is roughly in line with the other 12 known studies on intelligence in Sudan.

Friday, 27 February 2015

Your Google IQ

Most people are aware that asking a question can reveal ignorance, and out of fear avoid doing so in public, thus frequently remaining ignorant. They are not entirely wrong: by revealing exactly what they do not understand they allow other to make estimates of their intelligence. Hence the benefits of looking up things in private, on the internet.

I am a fan of everywhere, everytime, universal IQ tests: these are based on the notion that life is an intelligence test, and that estimates of ability can be drawn from all behaviours, even incomplete snippets of behaviour. I am on the lookout for research showing that IQ can be estimated from non-IQ test real world activities, of which asking questions is one.

The power of Google was first brought home to me by a little vignette. About 7 years ago I had gone to a vast warehouse called PC World, in an attempt to clear up some problems on a computer. They quoted me a price higher than the value of the actual device, but after I had remonstrated with them, told me in a whisper that there was a little place up the road which would do the job for half the price.

The small shop was sparse: a front room with some printers and a few laptops for sale, a back room for technical staff. The boss was an English countryman who presided over all with a kindly humour, dressed as if going out with his dogs; the technical assistant was a young Sikh with a warm but weary smile who confided to me, as he worked on my computer, that he had told the boss a hundred times that the “print a page for 20 pence and help locals with software” service was totally uneconomic and a real nuisance. Our consultation was interrupted by the hesitant entrance of a very short and frail old lady, unsteadily carrying a very large laptop. Once she got to the counter she lifted it up with some difficulty, glared at him; and said in accusing tone of voice:  “I’ve lost my Google”.

Presumably there is a difference between googling: “How do I extend my penis” and “Does Hilary Mantel know any history?” Can that difference provide IQ estimates?  Equally, can you distinguish between:  “Thuggish”, “Ruggish”,  “lamium” and “liatris”, and do any of these have predictive value?

McDaniel, Pesta and Gabriel (2015) Big data and the well-being nexus: Tracking Google search activity by state IQ. Intelligence 50 (2015) 21–29

https://drive.google.com/file/d/0B3c4TxciNeJZRjFrOElKSHdjZ0k/view?usp=sharing

The McDaniel team have dipped their fingers into the American soul by linking US State level google searches with state scholastic achievement levels to as to find the search items which best reveal intelligence, both high and low. I get the impression they found out much about their fellow citizens which they did not previously know (nor did I).

They used the Google Correlate algorithm (a database tracking billions of user
searches) to identify search terms that co-varied most strongly with U.S. state-level IQ and wellbeing. First, they identified the 100 strongest positive and negative search term covariates for state IQ. They then rationally clustered search terms into
composites based on similarity of concept, and correlated those composite scores with other well-being variables (e.g., crime, health). Search-term composite scores correlated strongly with all well-being variables.

We used state well-being data from Pesta et al. (2010), who created six sub-domains of global well-being: IQ, religiosity, crime, education, health, and income. IQ was estimated from public school achievement test scores (see McDaniel, 2006). Religiosity was derived from state-level survey data assessing fundamentalist religious beliefs (e.g., “My holy book is literally true;” “Mine is the one true faith”). Crime was created from various violence statistics, including burglary, murder, rape, violent crimes, and the number of inmates per capita. Education included the percentage of residents with (a) college degrees and (b) jobs in science, technology, engineering, or mathematics. Health included infant mortality and the incidence of obesity, smoking, and heart disease. Finally, income included income per capita,
disposable income per capita, percent of families in poverty, and percent of individuals in poverty.

McDaniel had already calculated estimates of IQ for the 50 US states. The authors note:  Aggregate IQ measures correlate strongly with many other meaningful variables. Examples include aggregate IQ predicting levels of institutional quality
(Jones & Potrafke, 2014), absolute latitude/temperature (León & León, 2014; Pesta & Poznanski, 2014), election outcomes (Pesta & McDaniel, 2014), economic freedom (Belasen & Hafer, 2012), religiosity (Reeve, 2009), crime (Templer & Rushton, 2011), education (Pesta et al., 2010), health (Eppig, Fincher, & Thornhill, 2011; Reeve & Basalik, 2010), and income (Lynn & Vanhanen, 2002, 2012). In fact, levels of religiosity, crime, education, health, and income are themselves largely inter-correlated within the 50 U.S. states.

We show that IQ and well-being covary with an activity ubiquitous in many
people's lives—conducting Google searches on the internet. Billions of Google searches are performed per day (Internet Live Stats, 2014). These searches provide snapshots of interesting human behavior. Moreover, many state well-being variables
are derived from self-report data (e.g., religious belief data, census survey data) that may be influenced by impression management and self-deception (Paulhus, 1991), in addition to potentially being affected by accuracy of memory and inattentive
responding. In contrast, the current study employs novel measurement methods (massive archival records of internet searches) that are not affected by typical problems inherent in self-report data. Our data are therefore both unobtrusive and non-reactive.

We report that some specific search terms co-vary in frequency with each state's relative level of IQ and well-being. We make sense of these correlations by using rational clustering, and by referencing extant literature to explain why the derived clusters might fall within the well-being nexus.

Now it is time to skip the methodological details (which these authors and their confederates relish) and peer ahead at the actual results. In Table A - 1 are the terms which show a positive relationship with intelligence. For the life of me I cannot understand why “mowing lawn” or “cricket rules” top the list. At least the 9th ranked search “lamium” is Latin, but what sort of intellect requires guidance on the boiling of an egg? We are talking State averages, I know, but these searches are a revelation to me.

 

image

Now we turn to searches which are associated with more modest intellects. I find these more cheerful, and somewhat more predicable. Eye-shadow tutorials indeed. Before long there will be Masters courses in the topic. Kitty shoes, clothes, and stuff is very interesting. You may already know this, but a Kitty shoe is like an ordinary shoe, but with “Hello Kitty” and a drawing of a kitty on it. To save you searching for it, I have copied it below. Sweet.

Image result for hello kitty logo

 

 

image

By now you will be asking yourself what “asvab” stands for: Armed Forces Vocational Aptitude Battery. Very sadly, wanting to read a simple guide as to how to do this test is not associated with high aptitude. However, it does show that the armed forces have learned about the importance of IQ the hard way, and have been given carte blanche to use IQ tests to reject as many candidates as fail to reach their standards.

I find this paper highly instructive. The authors have opened a new window on the mind. They would like to go beyond the 100 terms, and should be encouraged to do so when the data become available. With a bit of help from them I will be able to make significant additions to my “7 tribes of intellect” post. 

As to Hilary Mantel, the Wiki entry on Thomas Cromwell is a good place to start, and gives the major biographies. On a final point, I wish to make it absolutely clear that when I google “basic statistics for dummies” I am merely idly checking whether the procedures are being described with absolute accuracy. And a Goodbye Kitty to all of you.

Wednesday, 25 February 2015

An enquiry into civilisation: remembering lectures

In my clinical practice, although some researchers had claimed that traumatic amnesia was common, I found that my patients had vivid memories, often ones they wished to forget. I consulted memory man Prof John Morton, FRS, him of Logogens and Headed Records fame, and we were able to show that in a dreadful ferry disaster where almost half of the people drowned, survivors had almost perfect memory for who they were with immediately before, during, and after the terrifying event. The imminent prospect of death did not cloud their recall. Given the unusual fact that I had personally interviewed a large number of survivors, we were able to test their memories against the accounts of other survivors, and cross-validate them, a rare test of the accuracy of traumatic memories.

Thompson, J., Morton, J., Fraser, L. (1997). Memories for the Marchioness. Memory 5(5), 615-638doi:10.1080/741941482. Author URL

In one of our many conversations John Morton told me about an interesting memory experiment, in which participants were asked to read out the letters of a foreign language text, presented to them upside down. I hope you will agree that this denies them the usual contextual and linguistic cues which make ordinary text potentially easier to remember, because you can get some sense out of it, but you are denied the search for meaning in this task. A year later, without having been previously warned that this would happen, they were given the same task again. They completed it faster the second time. So, John Morton noted, perhaps almost everything can be remembered, even if it is hard to retrieve. The trace is always there. 

I can’t remember the reference, despite having written it down somewhere. Can anyone help me?

If traces remain of all events then it follows that I ought to be able to remember my first year university lectures, that is, remember them in the sense of having traces that should be easily summoned up by looking at the titles again. Perhaps it also means that I have always been guided by their content, without knowing it was happening, merely assuming that what I heard in those lectures was known to everyone, or at least to most people I knew. Common currency, and no big deal, but a point of unacknowledged reference, a scaffold on which conjectures and refutations can be sustained.

So, I decided to ask those who had sat through the same lectures to let me see their copies of the program. I can only find 1965 which was the year after mine, kindly sent by Marshall Colman. The Foundation Year course changed slowly, so it is probably an almost perfect match, and I can recognise most of it.

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In matters of detail, I think I had forgotten Prof Gemmell’s lectures on natural selection and inheritance though I may have been guided by the content, and remember his aphorism (from the Chinese): “One mountain, one tiger”; vividly remembered some of Prof Ingram on Physics (because of the practical demonstrations); and partly remembered Prof Ian Hunter on Psychology; Prof MacKay on computation and the measurement of information; and, to my surprise, had forgotten or rejected recalling the Christian farewell.

In the matter of surveying the broad picture 51 years after the event, recalling that year fills me with emotion. The founding Professors did their very best to educate me, and even though I took notes diligently, I wonder if I appreciated at the time what I was being given. After all, this was my only experience of university teaching, and I half-assumed it was the norm.  The Foundation Year was an enquiry into civilisation, a confident exposition of the Western heritage,  sufficient to let students read more widely, and provide them with reference points so that they knew how to ask questions on many subjects, and a framework to understand the scale if not detail of subsequent advances. It was a starting point on a journey which allowed them to speak as easily to Carl Sagan as to Douglas Adams.

Very belatedly, I’d like to thank Prof Lindsay for founding the University of Keele, where this course was taught to all undergraduates. Five years after I graduated it was deemed too expensive, since the bold experiment took up a whole year extra year, and required not only Heads of Department to prepare and give many lectures, but a much larger number of Lecturers to run weekly tutorials and mark all our essays. It became just an option, and continues only in reduced form.

Which universities still teach all undergraduates a course like the Foundation Year? Would you like to design a one suitable for the current time?

Tuesday, 24 February 2015

The Oscars for Intelligence

Last night the film business gave out prizes for actors, using a fallible voting system. Perhaps gross takings would be more valid, though more vulgar. The awards are always open to question, not only because of undue influence and general silliness, but because actors can only perform, and we do not have objective criteria to favour one over another.

At least 25 years ago I went to talk on a BBC radio program, You and Yours, and walked in to find that another of the interviewees was a famous actress, Jill Bennett, who had been married for 9 turbulent years to the playwright John Osborne, of Look Back in Anger fame. He did great things for the theatre and less good thing for his many women. After he had left her, Jill send him a lovely shirt for his birthday, with the inscription: “I want the contents back”. He did not return and she committed suicide in 1990. Anyway, there I was, facing this paragon of London theatre, the new thespian royalty, and I blurted out: “And what is your interview about?” She replied: “Putting bums on seats”.

Whilst we should probably measure actors by the number of bums they have put on seats, what harsh measure should we apply to intellectuals? For historical comparisons, In Human Accomplishment: The Pursuit of Excellence in the Arts and Sciences 800 B.C. to 1950 Charles Murray uses renown: the extent to which they are mentioned in encyclopaedias and scholarly references, and this works well. Some thinkers stand out: Galileo in Astronomy; Darwin in Biology; Newton and Einstein in Physics, Pasteur in Medicine; Euler in Maths. Oscars for all of them.

To a certain extent we can get a contemporary estimate of intellectual power by using a variant of chess rankings. The  beauty of chess for our purposes is that it is hard to play anyway, and even harder against a good opponent, and most of the time one person wins and another loses, with a few draws. There you have it: competitions generate a list of wins, and grandmasters play against grandmaster opponents who have themselves won most of their games. No quibbles: the champion meets the challenger, and the best player wins.

Instead of classical intelligence tests, can we conduct intelligence championships? For example, can we find the best chess players in the rankings, and note what characteristics they have in terms of other intellectual abilities? Chess rankings can be used to good effect to get real estimates of intelligence. For example, imagine a country where everyone is very strongly motivated to play chess, because it brings social and material advantages. The Government encourages chess playing across the nation, and encourages local, regional and national championships. Those chess players who do well get extra pay, housing, and a degree of freedom not allowed to other citizens. In such a setting, as in Soviet Russia from 1919 to almost the end of the century, who won the competitions?

You will see that La Griffe used chess as his first competition, and the Putnam maths competition as the second, and the winners are……Ashkenazis.

http://www.lagriffedulion.f2s.com/ashkenaz.htm

If life really is an intelligence test, then we should be able to get ability estimates from a broad range of behaviours, not just chess and maths, even if they are brief and interrupted segments of behaviour. A universal intelligence test should be capable of being applied anytime and anywhere:

Hernández-Orallo and Dowe (2010) Artificial Intelligence 174 1508–1539 Measuring universal intelligence: Towards an anytime intelligence test.

•The test should be able to measure the intelligence of any biological or artificial system that exists now or in the future.

•It should be able to evaluate both inept and brilliant systems as well as very slow to very fast systems.

•The test may be interrupted at any time, producing an approximation to the intelligence score, in such a way that the more time is left for the test, the better the assessment will be.

• It utilises the measurement of machine intelligence based on Kolmogorov complexity and universal distributions (a measure of the computational resources needed to specify an object, which were developed in the late 1990s (C-tests and compression-enhanced Turing tests).

But what if you don’t play chess, avoid maths competitions, and just like playing around with games on your computer? Can we get any ability estimates out of such a person, even if they won’t come in to be tested? So, has anyone tried to do this?

Han van der Maas and colleagues have made an excellent first step, developing a new computer adaptive intelligence test. They start with an item bank of over 500 maths problems, and then use an elegant technique derived from the Elo chess ranking system. In tennis and chess tournaments players are matched with opponents of same rating/ability: in adaptive testing ratings are estimated ‘on the fly’ and following the Elo system: “if I win my rating increases, the rating of my opponent decreases. If I win against a very good player my rating increases more”

What these researchers have done is to make the items compete with the persons. If you pass the item, the item loses and you win. Your score goes up, the item score goes down. Eventually each person is sorted against each item, and that can be done again and again. Beautiful.

Testing time is cut in half, repeated testing and practising on the test are allowed and encouraged, and the test can be used for a wide range of abilities. In fact, the old Binet test took exactly this approach, with fewer items, and a bright tester instead of a computer. This approach, disguised as a game, not only tests maths but the intelligence related subtests of: Proportional reasoning, Deductive reasoning, Number reasoning, Working memory and Perceptual reasoning.

To give you an idea of the reach of this technique: there are 120,000 active users in 1,400 schools, responding to 45,000 items at the rate of 1,200,000 items per day (yes, 1.2 million) cumulating in 400 million item responses over 5 years. As you will no doubt appreciate, this raises intelligence testing to a new level.

Have a look at the Powerpoint lecture, as presented to us at the ISIR conference in Graz by Han van der Maas

https://drive.google.com/file/d/0B3c4TxciNeJZTmJ2ZWo4V0J0cEE/view?usp=sharing

and then at the much more detailed paper which lets you see much further into the system.

https://drive.google.com/file/d/0B3c4TxciNeJZdGZEMkpVWE5WM1k/view?usp=sharing

If you are considering doing some research on large samples you might like to contact the team about doing some collaborative work with them. We haven’t yet sorted out Kolmogorov complexity and universal distributions, but if you know someone who is interested in this, get in touch.

Sunday, 22 February 2015

Steady as she goes

There is little point in reading newspapers when they pretend to discuss serious subjects, but even so, one hopes for the best. Two days ago an article in a broadsheet British newspaper offered “Seven ways to appear more intelligent than other people”. Not reading newspapers was not one of them.

http://www.telegraph.co.uk/finance/jobs/11418390/Seven-ways-to-appear-more-intelligent-than-other-people.html

However, these stories show what sticks in the mind: the ideas which get repeated because they serve the function of disparaging intelligence test results. “Scientists once claimed that intelligence quotient (IQ) levels were hereditary. This meant that human beings had no control over their brain power; it was decided by their genes. However, recent studies have shown that IQ scores are barely linked to genes at all. They can also be extremely volatile, changing significantly - by up to 20 points - over time.”

Ignoring the pure ignorance, it was the claim about “volatility by up to 20 points” that caught my eye. No reference was given, but in the 1970s that was already a popular argument. In other fora I found a 2012 paper being quoted in support of that claim, so that seemed worth a look.

Sue Ramsden, Fiona M. Richardson, Goulven Josse, Michael S. C. Thomas, Caroline Ellis, Clare Shakeshaft, Mohamed L. Seghier & Cathy J. Price. (2012) Verbal and non-verbal intelligence changes in the teenage brain. doi:10.1038/nature10514

http://www.psyc.bbk.ac.uk/research/DNL/personalpages/Ramsden_etal_2011.pdf

They tested 33 adolescents at 14 years and again at 18 years, each time giving them a Wechsler IQ test and an MRI. 33 adolescents are hardly a good representation of adolescents generally. Presumably the cost of MRI scans has limited the number, so the authors have tried to ensure that the people they selected represented the normal range. The same technique has often been used, for example in the early days of inspection time studies, when the testing procedure was very time consuming. Small, artificially representative samples were criticised then, and can be criticised now, but they are a start, though better for establishing whether a correlation exists than as a measure of normal variability.

The sample means were 112 (13.9) at first testing and 113 (14.0) at second testing, an overall gain of 1 IQ point.    There was what the authors call “a tight correlation across testing points (r = 0.79).

The wide range of abilities in our sample was confirmed as follows: FSIQ ranged from 77 to 135 at time 1 and from 87 to 143 at time 2, with averages of 112 and 113 at times 1 and 2, respectively, and a tight correlation across testing points (r = 0.79; P < 0.001).

At this point, you might want to stop reading. In social science research, correlations of 0.8 are very large and rarely found. This is a strong correlation, so intelligence tests are OK and worth using. Move on.

However, test-retest correlations over 6 months for the Wechsler are usually about 0.9 so this reported correlation is tight, but not tight enough. Adolescence is a time of change (though probably not as much as early childhood) so something is going on.

The authors say: strong correlations over time disguise considerable individual variation; for example, a correlation coefficient of 0.7 (which is not unusual with verbal IQ) still leaves over 50% of the variation unexplained. 

Call me picky, but they should have said “strong correlations include individual variation, because only with perfect correlation does individual variation disappear”. Nothing is being hidden. All scores contribute to the correlation statistic, even outliers. Earl Hunt accuses some researchers of being lawyerly rather than scholarly, and this is the way tricks are played: if you want to stress that IQ is OK, use correlation coefficients; if you want to stress that IQs are rubbish, use the one case with the biggest difference you can find. The same trick is played in the case of adoption and IQ: genetically inclined commentators reveal, truthfully, that years after adoption Black kid’s IQs correlated more strongly with their Black blood parents than with their White adoptive parents; environmentally inclined commentators reveal, truthfully, that the IQs of Black kids go up when White parents adopt them. Environmentalists champion the increase in IQ that Black children showed at age 7, because it was a big gain. They are less keen to reveal that by age 17, when the gain should have become even bigger (even more years for wealthy, middle-class White parents to pass on intellectual stimulation and good table manners to their Black adoptees) the gains had diminished, though not been entirely lost.

These selective presentations are very much like the “metric shift illusion” in which you can make a rare disorder seem common by saying how many sufferers there are in a large national population. Better to give the rate per 100,000 for all disorders, so that there is true comparability.

http://drjamesthompson.blogspot.co.uk/2013/07/disorders-of-brain-and-metric-shift.html

Incidentally, the results from this study are interesting: The results showed that changes in Verbal IQ were positively correlated with changes in grey matter density (and volume) in a region of the left motor cortex that is activated by the articulation of speech. Conversely, changes in Performance IQ were positively correlated with grey matter density in the anterior cerebellum (lobule IV), which is associated with motor movements of the hand. Post hoc tests that correlated structural change with change in each of the nine VIQ and PIQ subtest scores that were common in the WISC and WAIS assessments found that the neural marker for VIQ indexed constructs that were shared by all VIQ measures and that the neural marker for PIQ indexed constructs that were common to three of the four PIQ measures. This indicates that our VIQ and PIQ markers indexed skills that were not specific to individual subtests. There were no other grey or white matter effects that reached significance in a whole-brain structural analysis of VIQ, PIQ or FSIQ.

Later, they say: Specifically, 66% of the variance in VIQ at time 2 was accounted for by VIQ at time 1, a further 20% was accounted for by the change in grey matter density in the left motor speech region, with the remaining 14% unaccounted for. Similarly, 35% of the variance in PIQ at time 2 was accounted for by PIQ at time 1, with 13% accounted for by the change in grey matter density in the anterior cerebellum, leaving 52% unaccounted for. Future studies may be able to account for more of the between-subject variability by using a similar methodology with larger samples or other methodologies that measure structural or functional connectivity.

The attraction of this result for journalists is that it uses the minimum and maximum score difference statistic, which gives an inflated impression of variability. Even taking this study at face value,  the mean difference between IQ scores is precisely 1 point. The standard deviation of the change scores is 9 points which is 0.6 sd. To give the authors their due, they are on the hunt for discrepancies, and want to link them with brain changes. For once these different scores are being explained by some real data, rather than mere surmise about error terms.

However, the journalist has taken a phenomenon caused by the developing brains of 33 adolescents and then used the minimum and maximum changes of outliers to disparage intelligence testing.

What do test-retest score look like across the whole lifespan?

Ian J. Deary and Caroline E. Brett Predicting and retrodicting intelligence between childhood and old age in the 6-Day Sample of the Scottish Mental Survey 1947 Intelligence Volume 50, May–June 2015, Pages 1–9

http://www.sciencedirect.com/science/article/pii/S0160289615000203

In studies of cognitive ageing it is useful and important to know how stable are the individual differences in cognitive ability from childhood to older age, and also to be able to estimate (retrodict) prior cognitive ability differences from those in older age. Here we contribute to these aims with new data from a follow-up study of the 6-Day Sample of the Scottish Mental Survey of 1947 (original N = 1208). The sample had cognitive, educational, social, and occupational data collected almost annually from age 11 to 27 years. Whereas previous long-term follow-up studies of the Scottish mental surveys are based upon group-administered cognitive tests at a mean age of 11 years, the present sample each had an individually-administered revised Binet test. We traced them for vital status in older age, and some agreed to take several mental tests at age 77 years (N = 131). The National Adult Reading Test at age 77 correlated .72 with the Terman–Merrill revision of the Binet Test at age 11. Adding the Moray House Test No. 12 score from age 11 and educational information took the multiple R to .81 between youth and older age. The equivalent multiple R for fluid general intelligence was .57. When the NART from age 77 was the independent variable (retrodictor) along with educational attainment, the multiple R with the Terman–Merrill IQ at age 11 was .75. No previous studies of the stability of intelligence from childhood to old age, or of the power of the NART to retrodict prior intelligence, have had individually-administered IQ data from youth. About two-thirds, at least, of the variation in verbal ability in old age can be captured by cognitive and educational information from youth. Non-verbal ability is less well predicted. A short test of pronunciation—the NART—and brief educational information can capture well over half of the variation in IQ scores obtained 66 years earlier.

In sum, IQ scores hold up well. Steady as she goes. The score you get at 11 will be very similar to the ones you get at 77. Similar, but probably not identical. You could go out and hunt for a couple of people who have lost and gained the most IQ points just for the perverse pleasure of it, but why concentrate on the biggest discrepancy you can find for one individual when you can give the results for all individuals in one summary statistic: the correlation coefficient? If the latter is too difficult, why not get a ruler and a sharp pencil and try drawing the best line through a scatter-plot?

Monday, 16 February 2015

Turtles all the way down

 

Some people are fond of silly arguments. For example, that opium makes you sleepy because of its virtus dormitiva, as Moliere jested. For example, that people can see because the image cast onto the retina is looked at by an inner eye, which presumably also  has a retina. Instincts, drive states, and countless other  hypothetical constructs are very popular in psychological texts. Id and ego, for example, or black boxes and other dragons that are constructed to obscure the simple fact that most of the time we do not know what causes behaviour. Indeed, it sometimes seems that psychology isn’t possible, not real psychology anyway.

A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the centre of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: "What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise." The scientist gave a superior smile before replying, "What is the tortoise standing on?" "You're very clever, young man, very clever," said the old lady. "But it's turtles all the way down!" (Hawking, 1988, Brief History of Time, pp. 1, para 1).

If I had a £10 pound note for every paper I have read with a black box with arrows going in and out I would be writing this blog on the back of my yacht. Absent this income stream, I have decided to enter the modern commercial world by invoicing any colleague whose work I mention. First to be served with a bill under this new harsh regime is Rogier Kievit who innocently mentioned that in the introduction to his thesis he covers the issues of: the reduction problem; explanatory levels and the unity of science; the mind-body problem; and the dangers of greedy (neuro) reductionism.

Kievit quotes Oppenheim and Putnam’s (1958) proposal that science consists of a hierarchy of explanatory levels that range from those concerned with the ‘large’, or ‘high’ (e.g. social groups) to the ‘small’, or ‘low’ (e.g. atoms or subatomic particles). As entities at a higher level can be said to consist of (be made of) elements at the lower level, science consists of basic, physical building blocks that aggregate to form the hierarchy of sciences. They propose that theories at higher explanatory levels of psychology can be reduced to lower order levels of biology if and only if: 1) The vocabulary of psychology contains terms not in the vocabulary of biology 2) Any observational data explainable by psychology are explainable by biology 3) biology is at least as well systematized as psychology.

Kievit finds this somewhat lacking, and prefers Ernest Nagel’s (1961) suggestion that at every explanatory level, we can discover regularities, or laws, which describe the interaction of entities at that explanatory level (e.g. brain regions interacting). However, as the objects at a certain level (e.g. brains) consist of objects at a lower level (e.g. biochemical molecules), it should be possible to discover law-like statements that translate the regularities at one level (brain regions interacting) into the regularities at a lower level (properties of biochemical molecules). Nagel called such statements bridge laws. Ultimately, a complete specification of these bridge laws would allow us to do away with any ontological commitments other than of the units at the lowest level: The bridge laws would allow us to analytically translate any scientific regularity either ‘upwards’ or ‘downwards’.

He adds that Daniel Dennett (1995) distinguished between reductionism in general on the one hand, described as sensible attempts by science to explain larger units as parts of a whole, and greedy reductionism on the other. Greedy reductionism occurs when attempts are made to reduce phenomena at higher levels to lower levels across ‘large gaps’, without well-established intermediate steps. He uses the metaphor of a crane to represent a scientific or conceptual tool to translate or explain findings at one level from a level ‘down’. If one argues, on the basis of a physicalist perspective on the hierarchy of the sciences that the mind can (or should) be explained by physics or chemistry without establishing the solid intermediate steps required (cranes that can do the ‘work’), one is guilty of greedy reductionism. Similarly, we cannot simply proclaim that because the brain is necessary for psychological processes that all psychology can be reduced to the brain: We have to develop the scientific cranes that allow us to do the work of successfully reducing psychological phenomena to (increasingly) lower levels.

http://dare.uva.nl/document/2/138785

There, that plug should boost my assets by £10 which translates to four bags of coffee, or about a quarter of an inch of super-yacht teak decking. Now all I have to do is wait for the donations to flow in.

However, before I go, I should let Kievit off any need to donate anything more than that which he has kindly already done by sending me part of his thesis. The reason is that I have been trying to defend reductionism in general against greedy reductionism for quite some while, without knowing that last phrase of Dennett’s.

Years ago, in a restaurant near a conference venue, I sat down to dinner with a scholar who was concerned with the real world consequences of intellectual differences, with every prospect of us having a far ranging conversation about civilisations and intellectual classes. Another colleague joined us, and propounded the view that nothing much could be said about intelligence until we understood the physiological underpinnings at the cellular level. Time was precious, and I did not have Kievit’s as yet unwritten thesis in my hand, so I could not make accusations of greedy reductionism or call him to produce metaphorical cranes in defence of his views. Nonetheless, had I had the chance I would have said something like the following: 

Every measure has its range of convenience. The units used to measure fine tolerances of machine tools are not suitable for stating the distance between those machines on a factory floor, let alone the distances between towns. More importantly, computer machine code is not always the best method of discussing the relative merits of two different types of computer program. In that context we normally discuss the usability of the programs, their power in doing particular tasks, and the advantages and disadvantages of the way they depict the results. We use higher level concepts to discuss high level matters, without denying that computers use machine code.

Typically, different levels of analysis are used in psychological explanations for events at the cellular, organ, person and social level. Of course it is important to try to link them together, but we need to establish the solid intermediate steps required (cranes that can do the ‘work’). Even then, we will probably use explanations which are suitable for the level of our discussion. As Gilbert Ryle observed: Golfers can simultaneously observe the rules of gravity and the rules of the game.

So, here is my rather late statement to all persons skipping from one level of analysis to the other: please don’t jump from serotonin levels to battles between nations, from fMRI to brain states, and from brain states to emotions without doing the linkage work required.

Friday, 13 February 2015

Cigarettes, booze and beautiful women: the thin cut

From an early age, beautiful women plied me with cigarettes and alcohol. I can still remember their alluring scarlet-painted nails and perfectly tailored close fitting skirts as they reached towards me in a cloud of perfume, with bottles of whiskey and Salem menthol cigarettes in their immaculate hands. To add to the drama, there were clouds of the usual sort scudding past the windows of the battered DC-3 Dakotas and Short Sunderland flying boats I used to take between Buenos Aires and Montevideo, and air hostesses in close proximity could not fail to make a sensual impression on a 12 year old boy, sexual urges augmented by the excitation transfer of a bucketing aircraft with uncertain shuddering propellers battling thunderstorms across the River Plate.

By every environmentalist theory I should have been a natural drinker and smoker, with a perfect alibi for my excesses. Instead, I dutifully handed over the miniature bottles and 5 cigarette courtesy packs to my grateful parents. In later years I tried a few cigarettes, but they failed to ensnare me, and so I was never burdened by habits of the chemical sort.

Many other youngsters were not so lucky, and took up the seductive attraction of an illicit pleasure. Sure, it puts you at risk of lung cancer and general ill health, but why should it influence intelligence, when booze and fags are an intellectual’s necessities, or at least have often been touted as such, by intellectuals themselves if not by their doctors?

Some of you may be tired of hearing from the Craigleith sandstone citadel of Edinburgh, but I cannot stop the gang in that place from churning out interesting stuff. They find that smoking thins the brain, even when you allow for prior intelligence and other confounders, and that giving up smoking makes things better, but it takes the brain a long time to recover lost ground. It is a thin cut, but every millimetre counts.

Karama; Ducharme; Corley; Chouinard-Decorte; Starr; Wardlaw; Bastin and Deary (2015) Cigarette smoking and thinning of the brain’s cortex. Molecular Psychiatry advance online publication, 10 February 2015; doi:10.1038/mp.2014.187

They say:  Cigarette smoking is associated with cognitive decline and dementia, but the extent of the association between smoking and structural brain changes remains unclear. Importantly, it is unknown whether smoking-related brain changes are reversible after smoking cessation. We analyzed data on 504 subjects with recall of lifetime smoking data and a structural brain magnetic resonance imaging at age 73 years from which measures of cortical thickness were extracted. Multiple regression analyses were performed controlling for gender and exact age at scanning. To determine dose–response relationships, the association between smoking pack-years and cortical thickness was tested and then repeated, while controlling for a comprehensive list of covariates including, among others, cognitive ability before starting smoking. Further, we tested associations between cortical thickness and number of years since last cigarette, while controlling for lifetime smoking. There was a diffuse dose-dependent negative association between smoking and cortical thickness. Some negative dose-dependent cortical associations persisted after
controlling for all covariates. Accounting for total amount of lifetime smoking, the cortex of subjects who stopped smoking seems to have partially recovered for each year without smoking. However, it took ~ 25 years for complete cortical recovery in
affected areas for those at the mean pack-years value in this sample. As the cortex thins with normal aging, our data suggest that smoking is associated with diffuse accelerated cortical thinning, a biomarker of cognitive decline in adults. Although partial recovery appears possible, it can be a long process.

As you may know, I do not show pictures of brains on this blog, because they are apt to convince innocent readers of just about anything, but I urge you to make an exception for those created by Mark Bastin, which I am sending you under plain cover and you will find on pages 4, 5 and 6 of the paper.

https://drive.google.com/file/d/0B3c4TxciNeJZZGlyOE1OdlJnWlE/view?usp=sharing

However, I can reveal the picture that is worth 1000 words below, showing the full cost of cortical thinning for late quitters and current smokers:

 

 

image

 

"Smoking," wrote two-pack-a-day Jean Paul Sartre long before dying of lung failure at age 74  is "the symbolic equivalent of destructively appropriating the entire world." Perhaps those old smoke-wreathed intellectuals were dulling their bright minds with their habits, even though they could still turn a phrase which sounded profound. What damages the brain more: smoking or being a French Intellectual?

Monday, 9 February 2015

Philosophy of intelligence

 

On hearing any assertion my first thought is to wonder whether it is true or not. That strikes me as fundamental. I am well aware that I am likely to prefer some findings to others, and that I will be quicker to accept a finding which accords with my previous studies and what my tutors taught me, and with my personal inclinations, such as they are, though those change with age and experience.

However, if an assertion is untrue then, however attractive it may be to me, it is a falsehood and I must admit it, clear it from my mind, and say so in public. I wish that I were able to accept contrary findings as quickly as confirmatory ones, but that may come with maturity. Until then I confess I take some time to adapt my views to the new reality. Registering and quoting contrary research is the easy part, and can be done immediately. Taking down an explanatory mental framework takes a bit longer, but it happens before long, and it must for all of us, if we are to run our fingertips across the face of reality.

However, in terms of the academic ideal, once an idea is broken because the facts are against it, it is bust and that’s an end to it. Start again.

Some researchers take a different view. They say that some ideas, even if true, are not to be promulgated because they are dangerous. Naturally, this raises the question as to who decides whether an idea is dangerous. It gives precedence to the censor over the thinker. It requires that the thinker should always think of the censor, even when the censor may be imaginary.

Without much thought I have taken it as read that my readers will share a fundamental interest in truth, and saw no reason to belabour the issue. However, from time to time researchers argue in favour of taboo. I have been sent a philosophy paper which was something of an eye-opener, in that it showed me that a number of people still argue that to discuss group differences in intelligence is a moral error, to be avoided at all costs, even the cost of truth.

Nathan Cofnas (2015) Science Is Not Always “Self-Correcting” Fact–Value Conflation and the Study of Intelligence. Found Sci DOI 10.1007/s10699-015-9421-3

https://drive.google.com/file/d/0B3c4TxciNeJZbGt6eTgwTDlybEE/view?usp=sharing

In my view morality bites both ways: there are moral consequences from banning research as well as moral consequences from carrying out research, though the former consequences are often forgotten in the fears aroused by the latter. I take the simple view that it is better to know more than to know less, and that I do not want my curiosity to be curbed by other people’s love of ignorance.

I will give the author the last word, to prompt you to read his paper:

The scientific basis of eugenics was not discredited by the Holocaust any more than the theory of relativity was discredited by the bombing of Hiroshima. Nathan Cofnas.

Sunday, 8 February 2015

Prof Nick Mackintosh FRS (1935-2015)

 

So sorry to hear that Nick Mackintosh died today, the news carried in a tweet by Scott Barry Kaufman. I knew about him for ages only by repute, and then in the last few years by email exchanges, and only met him very recently, at Edinburgh when we were invited to the symposium on processing speed last May.

We had previously discussed Hans Eysenck (triggered by the memoir Mike Eysenck wrote about his father), and he agreed that notable psychologists like Hans sometimes had excellent early careers and then far from excellent late careers. (This did not apply to Nick). Nick also felt that when scientists became public figures their science suffered. He was thinking of a notable evolutionist, though only said this in a private exchange, more in regret than criticism. I think I got him to reconsider a letter he had had published in the Sunday Times about Robert Plomin, explaining that Robert had been misquoted, indeed, quotes had been fabricated. We traded views on intelligence research, and he was always kind and helpful, even when we differed considerably in our interpretations.

Only recently I came across a review in which he gently chided me for saying, too generously, that Richard Lynn’s views on sex differences in intelligence had been generally accepted, giving references to show me this was not so. I never got a chance to tell Nick that I accepted I must look at it again, and so delayed replying until I had something to send him, which ended up on my in-tray, and got no further.

It seems only a month or two ago that I shared a taxi with him and Pat Rabbitt, who commended me for getting out of the cab in a “sprightly” manner, to the wry amusement of them both. It seemed a very innocent joke at the time, and probably came about because I had told them I was unclear whether I had been invited to the symposium on ageing as a contributor or as an exemplar. I assumed Nick would be around for a long time.

105 years of the Flynn effect: very fluid

The Flynn effect seems to be continuing, or at the very least the publications on the Flynn effect seem to be continuing, so it may be that even psychologists are becoming cleverer, or simply more adept at publishing papers. Taking the former possibility as the kinder hypothesis, if everyone is getting smarter, it is about time we sorted out the Flynn Effect.

Even if we follow the less kind hypothesis, it is worthwhile maintaining an interest in the phenomenon of the secular rise in ability, because the apparent rise in intelligence test scores, without a particularly evident commensurate rise in everyday intelligence, is a topic worthy of critical analysis. Neither IQ tests nor scholastic attainment tests were designed for cross-cohort comparisons, so they might be suitable for a year-by-year identification of the brightest students without being able to give valid generation-by-generation comparisons. However, there may be some signs of increasing intelligence if the rising number of publications and patents are to be believed. More impressively, chess grand masters are getting younger.

Into this torrent of Flynn-Effectism jump Jakob Pietschnig and Martin Voracek with a large raft of a paper which runs to 179 pages, which is what you get when you have the temerity and the Teutonic thoroughness to plough through 105 years of data and assemble 271 independent samples from 31 countries, totalling almost four million participants.

What sorts of childhood do German speakers have, which drives them to these immense labours? Perhaps the Viennese duo of Jakob and Martin sat through early childhood, like Einstein, in mute bemusement at life. It is said (and even though this is apocryphal, I am repeating it) that Einstein did not speak until he was four, and then muttered “The soup is cold”. His family clapped and cheered and cried because they had been so worried about his muteness, and finally begged him to explain why he had never spoken before. Einstein replied: “Because formerly everything was in order”.

Pietschnig, J., & Voracek, M. (2015). One Century of Global IQ Gains: A Formal Meta-Analysis of the Flynn Effect (1909-2013). Perspectives on Psychological Science, in press.

http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2404239

Anyway, our two heroes have ploughed through more psychology papers than is fit to mention, and I am here to save you. In this case a picture is worth several thousand words:

 

image

So, the Flynn Effect is primarily on Fluid IQ and least on crystallised abilities, though still positive for those. We seem to have got brighter, particularly at on-the-spot thinking, though knowledge has increased as well. The prospects for humanity look good.

I wish I had the courage to end on that note, but there are one or two other things to mention, so as to do justice to this important paper:

IQ gains vary according to domain: 0.41 for fluid, 0.30 spatial , 0.28 full scale,
and 0.21 IQ points for crystallised. Effects are stronger for adults than children, and have decreased in recent decades. The authors suggest that factors associated with life history speed seem mainly responsible for the Flynn effect’s general trajectory, whereas favourable social-multiplier effects and effects related to economic prosperity appear to be responsible for observed differences of the Flynn effect across intelligence domains.

This formal meta-analysis of the Flynn effect provides strong evidence for continuous global generational IQ test score gains in the general population over the past century.

Gains were stronger between World Wars I and II, but showed a marked decrease during the World War II years: 0.72 vs. 0.21 IQ points annually.

There were decreasing gains in more recent decades. The decreasing strength of the IQ gains over time was reflected by meaningful negative effects of timespan for fullscale, fluid, and crystallized IQ, as well as year of onset for fluid and spatial IQ. Supported by the observed IQ change trajectories, evidence for decreasing gains in recent decades can be considered to be robust. Regression slopes of joinpoint regressions significantly decreased in the last segment of all IQ domains

Joinpoint regression analyses for all IQ domains showed a significantly better fit for regression models assuming changes in the strength of regression slopes over time than for models without incorporating changes in the slopes. This result indicates that IQ test score gains have not been linear over the past century, but rather seem to have been alternately accelerating and decelerating and finally decreasing during more recent years. Storfer already has proposed such changes in the strength of gains over time, estimating gains of 3.75 IQ points per decade from 1900 to 1920, of 2.50 from 1920 to 1960, and slightly smaller gains after the 1960s. In contrast, the present evidence indicates that a decrease in the strength of gains only emerged in the mid-1970s, yielding moderate gains of 2.30 IQ points per decade. However, the pattern preceding this period appears to be considerably more differentiated, indicating that gains during the early 20th century have been relatively weak (0.80 IQ points per decade), then showed a sharp increase in the 1920s (7.20 IQ points per decade), decreased again from 1935 to 1947 (2.10 IQ points per decade), but later again recovered until 1976 (3.00 IQ points per decade).

Stronger gains were observed for adults than children, showing large effects for fluid and spatial IQ (.28 and .66 respectively). Past research has attributed increasing gains with age mainly to effects of better education. If so, then educational effects would be expected to affect crystallized IQ most (e.g., Flynn, 2010). However, effects of age on crystallized and full scale IQ were negligible in the present study, although the signs of the change coefficients were directionally as expected.

GDP growth per capita was substantially positively associated with fullscale .09 , crystallized .18, and spatial IQ  .50, but showed negligible effects for fluid IQ. This finding is consistent with previous reports of links of economic prosperity with IQ in several nations (Lynn & Vanhanen, 2002). Associations between IQ gains
and GDP have been linked to educational improvements (Rindermann, 2008), thus conceivably reflecting effects of better educational infrastructure.

Comment: In my book only spatial shows a substantial correlation with GDP, and crystallised is merely indicative. Absence of an effect on fluid IQ is puzzling, suggests knowledge rather than wit is being boosted.

Stronger gains on low-g tests. IQ gains appeared not to be taking place on psychometric g. Findings of meaningful negative effects of medium and high g-ness of tests on IQ gains (.12 and .02, respectively) are supported by the overall lower gains observed in crystallized IQ (i.e., the domain with highest g-ness). These findings are consistent with previous evidence showing negative associations between g-ness and IQ gains (Te Nijenhuis & van der Flier, 2013) and corroborate the importance of environmental influences on generational IQ test score changes (Rushton, 1999)

The authors then go on to consider causes for the Flynn effect, and summarise them in Table 2, which I find too big on my screeen to constitute any sort of summary. It looks like a large traffic light. So, in linguistic, rather than tabular form, here is what they say:

At least three aspects of the present evidence support the role of education as an important contributing factor to the explanation of IQ gains: First, we observed substantial global increases in crystallized IQ. This may reflect, at least to a certain extent, effects of more and better schooling. Positive associations between crystallized IQ task performance and highest educational qualification are widely accepted and have previously been shown to be associated with gains on crystallized IQ measures. Nonetheless, although education has been shown to account for portions of crystallized IQ gains, gains have been reported to remain substantial after controlling for education (Pietschnig, Tran, & Voracek, 2013).

Second, larger IQ gains were observed for adults than for adolescents and children in fluid and spatial IQ domains. Surprisingly, no meaningful effect of age on crystallized IQ was found. However, this may be due to the effect of growing GDP which could mask age effects. Increasing numbers of average educational years may therefore explain stronger gains for adults than children.
However, although IQ test performance of children and adolescents has been observed to increase to a lesser extent than that of adults, gains for young samples still were substantial in our data. Although increases in formal educational years may not play a crucial role among children and adolescent IQ gains, increasing exposure to early childhood education programs, as witnessed in more recent years, might so. Although most such programs are aimed at more mature children, some of these programs are aimed at infants (e.g., the US-based ABCDerian project, which had average enrollment ages of 4.4 months; for an overview, see Hunt, 2011, pp. 288-291). Thus, even IQ gains in infants may be suitably explained by educational improvements. However, it remains difficult to decide the explanatory potential of early education programs for IQ gains in children and adolescents, because such programs differ considerably in coverage and availability between (and even within) investigated countries and timespans.

Third, IQ gains were predicted by average increases in GDP per capita across all domains, with the exception of fluid IQ. Positive associations of GDP with IQ gains have been observed in several studies and countries. In particular, the substantial effect of GDP on crystallized IQ may be linked to educational effects. It has been proposed that investments in better education lead to economic growth and vice versa, thus leading to a positive feedback loop of economic prosperity, education, and intelligence. Of note, it has been shown more recently that increases in GDP may be better described as a function of education rather than the other way round which in turn would reverse the causality assumption of the regression model applied by us. Regardless of the causality of the observed association, the positive sign of the association is consistent with this theory.

These findings show that there is little doubt that education plays a role in explaining the Flynn effect. Nonetheless, schooling is unlikely to account for the full extent of the IQ gains, and particularly the large gains for fluid IQ cannot be attributed to better education.

They say that there is little evidence that technology has a boosting effect. Neither has the decrease in family size, though the data are ambiguous about whether increased family size is a factor. Guessing in multiple choice settings is probably only a minor contributor at best, though consistent with the fluid IQ gains where guessing is most likely, because the items are difficult. Nutrition is discussed as a cause, but no clear confirmatory pattern emerges.

Although we did not directly test for decreasing IQ variability, findings suggest that at least nutrition and education may play an important role in this context and thus, consistent with prior research, may well have led to decreases in IQ variability.

Slower life history has been observed to be associated with a decline of the strength of g over time and promotes ability differentiation (Woodley, 2012a; Woodley & Madison, 2013). Consistent with the life history model, the Flynn effect in the present meta-analysis is apparently not on g. Indeed, the observed effects of test type suggest a negative association between IQ gains and psychometric g.
Predictions of the life history model appear to fit well to the observed patterns of IQ gains in the present meta-analysis. As this model does not warrant uniformity of changes across countries or strength of changes across time, life history speed would be suitable to explain the erratic pattern of IQ changes in our data. Different causes associated with life history speed could thus be either present or absent in single countries, but still would yield overall IQ gains due to compensatory effects of other factors being present. In other words, not all related causes need to be present in order to decelerate life history speed and consequently lead to gains; rather, causes may be effective one at a time.

Conclusion

I think this paper is a substantial step forwards, and gives a very well established broad based view of rising IQ scores. It will serve as an excellent source for many researchers, and considerably assist them in scoping putative causes. I have already stated my preference for raw data, individual items which serve as trace elements, particularly raw digit span scores and maths scores, where we can be more sure about the fundamental elements, as opposed to those crystallised accomplishments which are more subject to standardisation effects. However, the landscape of Flynn effect data have now been mapped out in great detail, and others will jump in to dig deeper into the rich archaeology which Pietschnig and Voracek have laid out for us in such detail.

I will give the authors the last word:

The totality of retrievable empirical evidence on this phenomenon, as quantitatively summarized here, points towards components of life history speed, such as improvements of education and nutritional factors as well as a reduction of pathogen-related factors, as the prime candidate causes of the Flynn effect, whilst differences in the strength of gains between intelligence domains may be accounted for by social multipliers and economic prosperity. Future research will show whether the now observed global decrease of IQ test score gains will ultimately lead to an end of these gains or even to a reversal.