Bryan Caplan  

Vegetarianism and Social Desirability Bias

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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.

COMMENTS (9 to date)
Joe writes:

I think a lot of pescetarians consider themselves vegetarians. I have several friends that consider themselves vegetarians, but will eat salmon or other fish. These same friends wouldn't consider eating red meat.

I wonder what the results would be if fish was excluded from the list of meats. These surveys might just be picking up on people being sloppy with language.

Chris H writes:

Part of the problem here is people using the wrong terms though. Many people who say they are "vegetarian" are actually pescetarians or think that only eating chicken counts as a form of light vegetarianism. They thus may not think they are wrong about being vegetarian (but they totally are).

Tom West writes:

At least from personal observation, vegetarianism is a continuum. Now I'd be surprised if people who called themselves vegetarian ate as much meat or as often as those who don't.

Still, if I'd been asked to guess as to percentage who'd eaten meat the previous day who'd called themselves vegetarian, I'd have expected the number to be around 20-25%.

JLV writes:

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Hazel Meade writes:

The signalling bias isn't because being a vegetarian is necessarily more socially desirable, or because you personally think vegetarianism is more morally right. It's because vegetarians generally care a lot more if someone else is a vegetarian, whereas meat eaters don't care very much.

Thus, there is a social premium placed on saying you're a vegetarian - all vegetarians in the room will like you more, but no meat-eaters will think less of you. So there is a small social advantage to be gained by the claim and little to lose.

IMO, a lot of people also claim to be vegetarians (or are vegetarians), because they like being catered to. The fact that the airline or the family friends have to prepare a special dish just for them gives some people a self-esteem boost.

JohnC writes:

VINOs everywhere.

"I think a lot of pescetarians consider themselves vegetarians."
I.e., most of India, Catholics during lent....

Jayson writes:

You can see the same sort of thing in our research (

"whereas only 15.6% of the public said they think low meat prices are more important than the well-being of farm animals, 67.5% said the average American thinks low meat prices are more important than the well-being of farm animals"

NZ writes:

The initial survey might have first asked,

Do you consider yourself to be a vegetarian?
And then, if the answer was "Yes," followed up with
Do you consider yourself to be a good vegetarian?
That would make the result of the follow-up survey more interesting.

MingoV writes:

Physicians also would not be shocked by the findings. Glucose logs by diabetics almost always contain falsified data. This was discovered by giving them new glucometers and asking them to record the results. The patients were asked to bring in their glucometers to be calibrated. The physicians also retrieved the stored results. The comparisons showed that over 99% of written logs had falsifications. The commonest excuses: I wanted my results to look better to please my doctor and I didn't want my doctor to know I wasn't doing all the finger sticks.

We were taught in medical school to be skeptical of anything said by patients or relatives. I have my own favorite question: Are you taking any herbal supplements or megadoses of vitamins? Most patients lie because they don't want their doctor to know they're self-medicating with "iffy" concoctions. The answer is import for medical reasons and lab testing reasons (some of the products interfere with lab tests).

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