Dietary Assessment Primer

Learn More about Reactivity

Reactivity occurs when individuals change their behavior due to awareness that their behavior is being or will be measured. Changes in behavior may include eating different types or amounts of foods than those usually consumed. [glossary term:] Reactivity may stem from a desire to simplify the reporting process (e.g., eating single foods rather than combination foods) or to comply with socially desirable norms (i.e., to avoid criticism or to appear to have a healthy diet). When an individual changes dietary behaviors due to reactivity, the resulting data may be accurate for the reporting period, but they do not reflect usual dietary intake. This is conceptually different from [glossary term:] misreporting (Learn More about Misreporting) of actual dietary intakes, which, among other causes, could arise from social desirability bias (Learn More about Social Desirability). Food records and pre-scheduled 24-hour dietary recalls (24HRs) are subject to reactivity because respondents know that their dietary intakes will be measured on a certain day and can change their behavior (see 24-hour Dietary Recall Profile and Food Record Profile). Unannounced 24HRs as well as food frequency questionnaires (FFQ) that query a long period of time in the past are not subject to reactivity, although misreporting may occur (see the Food Frequency Questionnaire Profile).

Some strategies can be used to reduce reactivity in dietary assessment instruments. Respondents can be asked to not alter their normal behavior, but the result of this instruction is unknown. If the instrument includes multiple days of report, analyses of systematic changes with time can inform researchers as to the extent and directionality of reactivity bias. Such an effect can be included in statistical modeling, but whether or not this eliminates reactivity bias has not been studied.

If the intent of dietary data collection is to monitor and reinforce dietary change efforts, using a food record as a behavior modification tool has been found to be very effective. In this case, reactivity may be a positive influence.