ABSTRACT
Consider this scenario:
A pharmaceutical company claims its new dietary supplement can change left-handed people to right-handers. Medical associations oppose the supplement on the grounds that it harms many people who use it. Noting that there is no reason for left-handed people to try to change, they urge their members not to recommend or administer the product to their patients. To test the drug company’s claim, a researcher conducts brief telephone interviews with self-proclaimed “ex-lefties.” He recruits respondents mainly through the drug company, which promotes his study to individuals who have given public testimonials about the product’s effectiveness. They say they tried the supplement because they felt miserable as left-handers in a right-handed world. Most claim they now function as right-handers, although many report occasional thoughts about using their left hand and some occasionally lapse into left-handedness. The researcher’s findings are based entirely on the one-time interviews in which he asked the ex-lefties to rate their handedness prior to taking the supplement (12 years earlier, on average) and during the previous year. Respondents’ ratings of their past and current handedness are significantly different. The researcher concludes that the supplement does indeed change left-handers to right-handers in some cases. Meanwhile, other researchers and clinicians report anecdotally that the food supplement does not change most lefthanders to right-handers, but many who tried the supplement report serious negative side effects.
