Illusion Chasers

Illusion Chasers

Illusions, Delusions, and Everyday Deceptions

Fat Tuesday: Insidious Weight Bias


Ed. note: This blog originally appeared on

I just want to thank you all for being so even-minded and fair when it comes to your attitudes about fat people. Or are you? According to a landmark study by Brian Nosek and his colleagues working with the inventors of the Implicit Association Test (IAT), Anthony Greenwald and Mahzarin Banaji, you actually probably aren’t. So I take back my thanks, you bigot.

The IAT is a wonderful tool to assess implicit associations between two concepts (like fat and thin) and two attributes (like good and bad). The experimenter displays, for example, a picture of a fat person and the word “bad” and the observer’s job is to simply press a keyboard button, as fast as possible. Images may be sorted according to four categories (thin/good, thin/bad, fat/good, or fat/bad). When you see 40 trials of these examples (10 for each association), what you find is that people tend to answer more quickly for concepts that are associated well with the attribute (i.e. fat/bad and thin/good) whereas they slow down in responding to concepts that are mismatched to the attributes (i.e. fat/good and thin/bad). This happens even if the observer self-reports as unbiased, or even if the observer has the attribute discriminated against (in this case, implicit association bias affect even people who are obese). What’s especially interesting about weight attitudes is that the bias works against ingroup matches. An outgroup is a social group that you consider to be different to you (i.e. fat people are an outgroup if you consider yourself thin). In most IAT tests of attitudes observers have positive attitudes towards their ingroup members. For example, Americans tend to see other Americans as part of the same ingroup and reflect on them positively, whereas foreigners are seen as members of an outgroup and produce longer delays in response in the IAT. But the study shows both fat and thin people (69%) preferred thin people over fat people on the IAT (only 12% of respondents liked the fatties).

So this suggests that if you are fat there is likely bias working against you, from the people closest to you. Even yourself.


The views expressed are those of the author and are not necessarily those of Scientific American.

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