DIETARY ASSESSMENT INSTRUMENTS ARE SUSCEPTIBLE TO INTERVENTION-ASSOCIATED RESPONSE SET BIAS

Objective Evaluations of trials of the effectiveness of dietary interv ention programs may be compromised by response set biases, such as tho se attributable to social desirability. Participants who receive a beh avioral intervention may bias their reports of diet to appear in compl iance with intervention goals. This study examined whether responses t o standard dietary assessment instruments could be affected by a brief dietary intervention. Design We assigned 192 undergraduate students r andomly to (a) see a 17-minute videotape on the consequences of eating a high-fat diet or a placebo videotape on workplace management and (b ) receive preintervention and postintervention assessments or only pos tintervention assessment. Dietary assessments included 4 independent m easures of fat intake. Results Among women, bias (intervention minus c ontrol) was -9.7 g fat (from a short food frequency questionnaire) and -0.6 high-fat foods (from a questionnaire about use of 23 foods in th e previous day) (P<.05 for both). No results were significant among me n or for 2 instruments that measured more qualitative aspects of fat-r elated dietary habits. Applications Even a modest dietary intervention can affect responses to dietary assessment instruments. Nutritionists should recognize that assessment of adherence to dietary change recom mendations, when based on dietary self-report, can be overestimated as a result of response set biases.