Vegetarianism and Social Desirability Bias
By Bryan Caplan
Economists love to dismiss surveys: “You can’t believe what people say. You have to look at what they actually do.” Yet we rarely bother to actually demonstrate the unreliability of surveys. Economists may be pleased to know, then, that two big surveys demonstrate a massive gap between words and deeds. The topic: vegetarianism:
The reason for the widespread but mistaken belief that America is rapidly going veg is the mismatch between what people say they eat and what they actually
eat. Take a 2002 Times/CNN poll on the eating habits of 10,000
Americans. Six percent of the individuals surveyed said they considered
themselves vegetarian. But when asked by the pollsters what they had
eaten in the last 24 hours, 60% of the self-described “vegetarians”
admitted that that had consumed red meat, poultry or fish the previous day. In another survey,
the United States Department of Agriculture randomly telephoned 13,313
Americans. Three percent of the respondents answered yes to the
question, “Do you consider yourself to be a vegetarian?” A week later
the researchers called the participants again and this time asked what
they had eaten the day before. The results were even more dramatic than
the Times/CNN survey: this time 66% of the “vegetarians” had eaten
animal flesh in the last 24 hours.
Economists may be shocked by the sheer size of the word-deed gap. But do you know who won’t be? Psychologists. Despite economists’ stereotypes, psychologists aren’t just well-aware of the unreliability of mere words; they empirically study variation in the reliability of mere words. The vegetarian results are classic cases of what psychologists call Social Desirability Bias. (And, Robin might add, Construal Level Theory). Long story short: Many people see vegetarianism as a moral ideal, but bacon tastes good. In such situations, Social Desirability Bias leads human beings to say they do the right thing, but do what feels good.
The lesson, however, is not that all words are unreliable. After all, how did the surveys find out what people actually ate? By asking them. The lesson, rather, is that some words are better than others. If you ask people about their dietary philosophy, meat-eaters with vegetarian ideals will probably claim to be vegetarians. But if you ask people what they ate yesterday, they’ll probably tell you the truth.