Sunday 7 August 2016

Myths dispelled, new myths propagated


It is a familiar journalistic trick to make a list of popular myths and then dispel them. One example is “50 Great Myths of Popular Psychology: Shattering widespread misconceptions about human behaviour” by Lilienfeld, Lynn, Ruscio and Beyerstein 2010. The authors are university psychologists of professorial rank, with active research careers, and their identification of myths and their attempted refutations are often entertaining. I am glad that some weak arguments have been exposed, and some popular beliefs revealed to have little research foundation, or to at least have foundations which can be questioned.

However, my view is that the “myths refuted” style of thinking is a prescription for poor science. In the late Earl “Buz” Hunt’s marvellous phrase, it leads to a type of argument which is “lawyerly” rather than “scholarly” because once you have identified something as a “myth” then you are honour-bound to destroy it, even if part of it is true.

So, I am going to look at one of Lilienfeld et al’s arguments from the point of view of argumentation and fact. Since the items are short, I will give their substantial arguments in full.

Myth 43 Most mentally ill are violent.

First, note the absolute nature of the myth: what is being dispelled is that a majority of mentally ill patients are violent. The myth is presented in exaggerated form, as a straw man, thus obscuring an important issue. What people fear is that mentally ill people are more violent than mentally well people, and on that basis it may be prudent to avoid them.

Second, the relevant question is “are mentally ill people more violent than mentally well people, and if so by how much?”

A third relevant question is whether the most-focussed-upon disorder within mental illness, schizophrenia, makes people more violent, and if so by how much? 

Prospective studies of mentally ill people will give the answer. An associated question, though not strictly relevant to the main issue, is whether violence can be predicted by concentrating on a particular sub-set of the mentally ill, or particular behavioural indicators. Here are the key arguments from Lilienfeld et al.

Yet commonplace public beliefs about mental illness and violence don’t square with the bulk of the research evidence (Applebaum, 2004; Teplin, 1985). Admittedly, most studies point to a modestly heightened risk of violence among people with severe mental illnesses, such as schizophrenia and bipolar disorder, once called manic depression (Monahan, 1992). Yet even this elevated risk appears limited to only a relatively small subset of people with these illnesses. For example, in most studies, people with paranoid delusions (such as the false belief of being pursued by the Central Intelligence Agency) and substance abuse disorders (Harris & Lurigio, 2007; Steadman et al., 1998; Swanson et al., 1996), but not other mentally ill people, are at heightened risk for violence. Indeed, in some recent studies, severely mentally ill patients without substance abuse disorders showed no higher risk for violence than other individuals (Elbogen & Johnson, 2009). Nevertheless, psychiatric patients who take their medication regularly aren’t at elevated risk for violence compared with members of the general population (Steadman et al., 1998). There’s also some evidence that patients with “command hallucinations”— hearing voices instructing a person to commit an act like a murder— are at heightened risk for violence. (Junginger & McGuire, 2001; McNiel, Eisner, & Binder, 2000).

Still, the best estimates suggest that 90% of more of people with serious mental illnesses, including schizophrenia, never commit violent acts (Hodgins et al., 1996). Moreover, severe mental illness probably accounts for only about 3-5% of all violent crimes (Monahan, 1996; Walsh, Buchanan, & Fahy, 2001). In fact, people with schizophrenia and other severe mental disorders are far more likely to be victims than perpetrators of violence (Teplin, McClelland, Abram, & Weiner, 2005), probably because their weakened mental capacity renders them vulnerable to attacks by others. Furthermore, most major mental disorders, including major depression and anxiety disorders (such as phobias and obsessive-compulsive disorder), aren’t associated with a heightened risk of physical aggression.

Notice the form of the argument: a modestly heightened risk of violence among people with severe mental illnesses, such as schizophrenia and bipolar disorder. Fine, but it would have been better to state the risk compared to the normal population risk. This way the reader has to chase up the references. Start with Applebaum 2004. In fact this is a letter by J.S. Appelbaum. On examination it has no actual data to contribute. Quoting it as a reference is feeble, and immediately calls into question the notion that these authors are in a position to challenge “myths”.

Next, Teplin (1985). This is better, in that it contains data, and arguments about the link between mental illness and criminality. Teplin rejects the obvious approach, which is to take a set of people who have been given in-patient treatment for mental illness, and then see what their subsequent criminal records are, compared with the general population. I will call this the epidemiological paradigm: “study psychiatric patients and see whether they commit crimes later”. Instead she plumps for what is in my view a more complex and error-prone approach, which is to look at the behaviour of those who come into contact with the Police at criminal incidents, as part of a larger study on how the Police dealt with mentally ill people. Psychologists went with the police to disturbances, and rated citizen behaviour for signs of :

severe mental disorder, e.g., confusion/disorientation; withdrawal/unresponsiveness; paranoid, inappropriate, or bizarre speech and/or behavior; and self-destructive behaviors

As you can see, this is back to front. Instead of following a defined population, people known to have had mental illness, and then seeing how many of them commit criminal acts, this study looks at people who are interacting with the police (criminals, victims, bystanders) and tries to determine how many of them are in the midst of an episode of severe mental disturbance. The defined base population has been lost, and things have to be estimated from the population of “people of interest to the Police”, a far weaker method.

Here are the results, as presented in the paper:


Mental disorder and criminality

Describing this table, Teplin says this of those with severe mental disorder:

they were somewhat more likely, 35.3 versus 23.4% for non-mentally-disordered persons, to be suspects.

Somewhat more likely? 50% more likely. However, this is to misunderstand the table, which has nothing to say about how many psychiatric patients go on to commit crimes. It does not tell us whether the 85 severely disturbed persons are what you would expect among 2122 citizens. At 4% of the population this is quite a high rate of severe mental illness. For example, lifetime prevalence of  all psychotic disorders was judged to be 3.06% in 2007 in US populations. So, there may be a 33% over-representation of disturbed persons in this police sample. Frankly, the method is too weak for any firm conclusions, though even this weak method shows mentally ill persons to be over-represented as suspects of crimes, by 50%.

Teplin goes on to say:

mentally disordered citizens made up less than 5% of the persons who were involved with the police.

She gives the median rate of severe disorder as 1.7% so her observed rate is 3 times higher! She gets out of this by saying that the study area included some neighbourhoods with more mental patients, ignoring that that is what you would expect from psychotic downward social drift. Her task was to find out whether mentally ill people committed more crimes than average, not to find out where they lived.

Teplin keeps making the irrelevant point (irrelevant to the issue of whether mentally ill people commit more crimes) that most interactions of mentally ill people with the police are not about violent crimes. This obscures the finding of interest. Here is her second table, about the suspects themselves:



Mental disorder and type of crime

On her own figures, severely mentally disordered persons are 3 times more likely to have been the perpetrators of violent personal crime. However, since we do not have proper base rates on a defined population of mentally ill persons all we can say is that they appear to be higher, and it could be a chance finding. This study does not confirm that severely mentally disordered persons are no different from the normal population, though the sparse evidence points the other way.

In an attempt to make their case, Lilienfeld et al say:

Still, the best estimates suggest that 90% or more of people with serious mental illnesses, including schizophrenia, never commit violent acts (Hodgins et al., 1996).

That means that 10% do commit violent acts. What is the rate for those without serious mental illness? In the US in 2012 total violent crime was 387 per 100,000 which is a rate of 0.39%. On that reasoning the violence rate for the seriously mentally ill is 10/0.39 = 25 times higher. I think that this is probably an error, even though it is presented as a reassurance. A comment as silly as that was reportedly made by a former president of the Royal College of Psychiatry, though certainly not the present one.

A final comment from Teplin:

In an exhaustive review of the pertinent research literature, Monahan and Steadman concluded that if a number of socio-demographic factors known to be related to crime are taken into account e.g., race, age, and prior criminality, the relationship between mental disorder and criminality substantially diminishes.

I think that sums up the problem with these arguments: someone with mental disorder and a criminal record is given statistical “time off” for previous crimes, even though they may have been caused by mental disorder. “Taking into account” becomes a form of washing them away from the causal nexus. In my view, this is very silly, and Monahan, Steadman and Teplin must know that, or at least acknowledge that “taking into account” covariates can be a misleading procedure. Before “correcting” any finding, the assumptions behind the correction should be made explicit.

Lilienfeld et al continue: Moreover, severe mental illness probably accounts for only about 3-5% of all violent crimes (Monahan, 1996; Walsh, Buchanan, & Fahy, 2001). In fact, people with schizophrenia and other severe mental disorders are far more likely to be victims than perpetrators of violence (Teplin, McClelland, Abram, & Weiner, 2005), crimes (Monahan, 1996; Walsh, Buchanan, & Fahy, 2001). In fact, people with schizophrenia and other severe mental disorders are far more likely to be victims than perpetrators of violence (Teplin, McClelland, Abram, & Weiner, 2005),

So, do the other studies follow the epidemiological paradigm?The other papers mentioned by Lilienfeld et al. are interesting in that they identify the patients who are most likely to be violent: patients with command delusions who have not taken their medication. How violent are they? The rates are not given. 

Are there other relevant papers Lilienfeld et al. could have mentioned, particularly those done the right way round: identifying the mentally ill and then checking whether they are involved in violent acts?

For a fuller review see:

For more recent research, admittedly after the publication of the myths book, but making the same point:

So, the myth is not a myth: schizophrenic patients are roughly 5 times more violent than the general public. It is up to you whether you want to avoid them on that basis.

The rest of the Lilienfeld “myths” book has many myth-busting chapters with which I either agree or want to agree. However, I haven’t checked the references, so I cannot be sure whether these myths have been dispelled or propagated.


  1. I wonder: How well do Lilienfeld et al. make the case that most people believe that a majority of mentally ill people are violent?

    I'm asking as experience suggests this journalistic format is often rich in straw men.

    1. Agree. They mostly talk about movies, and depictions of mad murderers. However, they then back up their views by quoting several surveys, so they at least prove there is an association, though no mention of a "majority".

    2. Thinking about it some more, I wonder whether there's not a semantic issue here. Depending on context, the term "mentally ill" might indeed make people think of folks who have Satan talking to them in their heads. But if you look at the rather inclusive definition that psychologists use, most "mental illnesses" are pretty mundane stuff.

      So, if you'd really want to do a survey, you'd probably want to go beyond the term "mentally ill" and describe some specific patterns of symptoms. Assuming you're disinterested, that is.

  2. If I were asked whether I believed that the majority of mentally ill people are violent, I'd probably reply that it depends what you mean by "mentally ill". Which is why I never co-operate with opinion polls: their questions are always far too simple-minded.

  3. You compared lifetime (10%) rates to annual rates (0.39%). Lifetime rates are going to be much much higher as they include decades of time.

    It's pretty funny that the authors cite Hodgins 1996 as evidence that the mentally ill don't have an increased risk of violence. I believe the study they're referring to is "Mental Disorder and Crime":

    Relevant info in Table 4. The authors calculate a relative-risk of 3-15 for those who have been hospitalized for a mental illness to commit a violent crime (varies widely by sex and diagnosis). It does seem like about 10% of mentally ill men (again, varying somewhat by diagnosis) go on to commit a violent crime.

    Relative rates are very different from absolute rates. I wouldn't care if the iced tea I drink increases my risk of shark-bites by 100x, because the risk is already so low. But I wouldn't drink it if it increased my risk of heart attack by 3x.

    I agree with your closing sentiment, people should make their own judgements about who to avoid (or not). In making that decision they should be aware of both absolute and relative risks.

  4. That schizophrenics are quite dangerous is very evident in the US from anecdotal evidence related to non-gangbanger crimes, so like most stereotypes, I accepted it as having a basis. The research backs it up....but academia in the US isn't very concerned with truth any more....

    1. ''That schizophrenics are quite dangerous''

      Dangerous is a people who lies in a infinitesimal cynical way and push wars and conflicts


      ''they'' don't seems ''schizophrenic'', they seems pretty aware about its attitudes, ;)