Friday 12 September 2014

Fat prejudice and slim conclusions


With the Woodley challenge on correlation still reigning supreme, what are we to make of a correlation between perceived prejudice against fat people (as reported by fat people), and their subsequent weight gain?

Of the 2,944 eligible participants in the study, 5% reported weight discrimination. This ranged from less than 1% of those in the ‘normal weight’ category to 36% of those classified as ‘morbidly obese’. There are somewhat more women in the fat category. Men and women reported similar levels of weight discrimination.  Those who reported prejudice were already fat, as weighed 2 years before; then gave their estimates as to whether they had been subjected to negative treatment (without actually having to say that it was on account of their being fat); and were then weighed 2 years later; by which time four years had passed and they had gained 0.95 Kg in weight, whereas the majority, who had not reported unfriendly treatment, had lost 0.71 Kg in weight.

They were all drawn from the English Longitudinal Study of Ageing, so we have a large and representative sample of over 50 year olds, and need not worry on that score.

Sarah E. Jackson, Rebecca J. Beeken and Jane Wardle. Perceived Weight Discrimination and Changes in Weight, Waist Circumference, and Weight Status 

Objective: To examine associations between perceived weight discrimination and changes in weight, waist circumference, and weight status.
Methods: Data were from 2944 men and women aged 50 years participating in the English Longitudinal Study of Ageing. Experiences of weight discrimination were reported in 2010-2011 and weight and waist circumference were objectively measured in 2008-2009 and 2012-2013. ANCOVAs were used to test associations between perceived weight discrimination and changes in weight and waist circumference.
Logistic regression was used to test associations with changes in weight status. All analyses adjusted for baseline BMI, age, sex, and wealth.
Results: Perceived weight discrimination was associated with relative increases in weight (11.66 kg, P<0.001) and waist circumference (11.12 cm, P50.046). There was also a significant association with odds of becoming obese over the follow-up period (OR56.67, 95% CI 1.85-24.04) but odds of remaining obese did not differ according to experiences of weight discrimination (OR51.09, 95% CI 0.46-2.59).
Conclusions: Our results indicate that rather than encouraging people to lose weight, weight discrimination promotes weight gain and the onset of obesity. Implementing effective interventions to combat weight stigma and discrimination at the population level could reduce the burden of obesity.

So, let us look at this work from the Woodley perspective of correlation and causation. We have fat persons and normal weight persons. These probably differ in many ways, which probably include intelligence and personality, social class and wealth, and genetics. We could study these differences, including looking at how many people in each category report prejudice.

I have already discussed some of these matters in “Fat is an intellectual issue” and “Diet is an IQ test”

However, the authors do not compare fat and normal weight people. They compare those that report prejudice versus those who do not. They find that the prejudice reporters are fatter and poorer than the large majority who do not report prejudice. Then, they conclude:  Our results indicate that rather than encouraging people to lose weight, weight discrimination promotes weight gain and the onset of obesity.

How do they conclude that?

Senior author Professor Jane Wardle, director of the Cancer Research UK Health Behaviour Centre at UCL, is reported as saying: “Our study clearly shows that weight discrimination is part of the obesity problem and not the solution. Weight bias has been documented not only among the general public but also among health professionals; and many obese patients report being treated disrespectfully by doctors because of their weight. Everyone, including doctors, should stop blaming and shaming people for their weight and offer support, and where appropriate, treatment.”

It is a bit of a jump from a person feeling discriminated against, to concluding that they have actually been named and shamed.

Dr Sarah Jackson said: “Most people who are overweight are aware of it already and don’t need it pointed out to them. Telling them they are fat isn’t going to help - it is just going to make them feel worse.

“There are lots of different causes of obesity, yet a lot of blame just seems to be on individuals and a lack of will power. Raising awareness of some of the factors involved might make it easier not to blame people.”

In deference, I should say that although all three authors are credited with this argument, one or more of them know it to be in error, because in the paper itself they say: We cannot be sure whether discrimination preceded weight gain or vice versa. It is therefore not possible to establish causal relationships; i.e. whether people gain weight as a consequence of experiencing weight discrimination, or whether gaining weight makes people more likely to experience weight discrimination or attribute experiences of discrimination to their weight.

The Press Office at UCL correctly say: “Because this was a population survey and not an experimental study, it cannot conclusively confirm that the positive association observed between discrimination and weight gain is causal”. However, they still give it the headline ‘Fat shaming’ doesn’t encourage weight loss and the Press have picked that line as their lead in widespread reporting.

Notice the obvious: a person’s perception that they are being treated unfairly (probably because of being over-weight) is not an objective measure like their weight. They may be being over-sensitive. Their perceptions about unkind treatment may be part of a set of distorted judgments about food, body image and self worth. The measures taken do not allow us to come to any judgment about this. Neither are there any intelligence or personality measures, which would have been instructive, even if they showed no difference, because we could have discarded them as possible causes of the difference.

Remember, the perception that “people treat me badly (probably because I am fat)” is held by only 0.7% of normal weight people (interesting it should be that high) but as many as 36% of the very fat people. I assume that a Chi square would reveal a strong association between heavy weight and perceived prejudice.

Let us compare the 150 people who report prejudice against them with the 2794 people who do not. The differences are shown in terms of p values, but this reliance on statistical significant might obscure the sizes of the differences. They do not differ in height. They differ massively in weight: 97 Kilos versus 75 Kilos. Just pause a moment on those figures. That is an effect size of 1.44. Wow. The no-discrimination group are hardly slender, with a BMI of 27.17 where 25 is the official preferred figure (and in fact 22 is the most conducive to normal health). The discriminated against have an average BMI of 35.46 They are also quite a bit poorer. Do they differ in intelligence or personality? Likely, but no measures of these variables are given.

Incidentally, the authors assume that not liking fat people is a fallacious pre-judgement. The also assume that “fat-shaming” is actually widespread as an activity. Fat avoiding is part of freedom. So is thin avoiding. So is avoiding psychologists. Preferences must not always be crimes.

I think that the authors have shown caution in the paper, but far less caution in their public statements as to what is in the paper. Perhaps their cautions were ignored, but the UCL Press Office is punctilious in letting authors vet their own statements for use by the Press. Of course, being unkind to over-weight people is uncivil and bad manners. One should not even be uncivil to psychologists. However, I think that it would have been better to report the correct conclusion:

People who think that others are prejudiced against them because they are fat don’t lose weight.

1 comment:

  1. Groß Inhalt. Ich schätze immer diese zuverlässige Informationen von Ihnen.
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