Does level of specificity affect measures of motivation to comply? A randomized evaluation.

The theory of planned behavior (TPB) is a popular value-expectancy model in social and behavioral health. Motivation to comply, one of the theory's constructs, has not been well operationalized and measured in the past, and to date, there has been no assessment of whether level of specificity affects the measurement of the construct. The purpose of this study was to measure the motivation to comply construct across four domains (from general to TACT-behavior specific) and evaluate the potential impact the differences have when identifying determinants of generalized injunctive norms. Students (n = 234) attending a large southwestern university completed a TPB survey related to sleep and physical activity, and were randomized to one of four domains that measured motivation to comply (General domain, n = 58; Health domain, n = 60; Behavioral domain, n = 56; and TACT domain, n = 60). Across both behaviors, motivation to comply measurements did not appear to be affected by changing the level of specificity. Referents for sleep and physical activity were mostly significant, but the effects were small to medium. Future researchers should consider removing motivation to comply measures from TPB surveys to reduce respondent burden or find alternative ways of measuring the construct.