One of the improvements we’ve instituted at the Cleveland Chiropractic College clinics is that all new patients now fill in the Physical Activity and Nutrition (PAN) form, which asks a dozen or so questions about exercise and diet. One question asks how many servings of vegetables the patient eats on an average day. If the answer is fewer than three, the student intern must speak to the patient about the importance of increasing their vegetable intake.
As noted in this New York Times article, such questionnaires have a built-in flaw: they rely on the truthfulness of the person answering the questions. Many people know they’re supposed to eat vegetables (or exercise frequently, or consume fewer sugary beverages), and don’t want to admit their failures.
Researchers from the University of Colorado in Denver randomly selected 163 women who were recruited by telephone and told they would be taking part in a general health survey. Half the women were sent a letter describing the survey as a study of fruit and vegetable intake. The letter included a brief statement of the benefits of fruits and vegetables, a Five-A-Day sticker and a Five-a-Day refrigerator magnet. The rest of the group received a general letter, without mention of fruits, vegetables, stickers or magnets.
When the questionnaires arrived, the group pre-primed to expect a focus on fruits and vegetables reported about double the intake reported by those who had not received the heads-up.
Does this mean such questionnaires are useless? Hardly. But it does mean that we need to assume that many of our patients aren’t quite giving us the whole truth and nothing but the truth. The technical term for this is “approval bias.” Awareness of such a bias in patients is important for those seeking to help patients to practice prevention.
