Background:<bold> </bold>A large number of modifiable and measurable daily actions are thought to impact mental health. The "Things You Do" refers to 5 types of daily actions that have been associated with mental health: healthy thinking, meaningful activities, goals and plans, healthy habits, and social connections. Previous studies have reported the psychometric properties of the Things You Do Questionnaire (TYDQ)-21-item (TYDQ21). The 21-item version, however, has an uneven distribution of items across the 5 aforementioned factors and may be lengthy to administer on a regular basis. Objective:<bold> </bold>This study aimed to develop and evaluate a brief version of the TYDQ. To accomplish this, we identified the top 10 and 15 items on the TYDQ21 and then evaluated the performance of the 10-item and 15-item versions of the TYDQ in community and treatment-seeking samples. Methods:<bold> </bold>Using confirmatory factor analysis, the top 2 or 3 items were used to develop the 10-item and 15-item versions, respectively. Model fit, reliability, and validity were examined for both versions in 2 samples: a survey of community adults (n=6070) and adults who completed an assessment at a digital psychology service (n=14,878). Treatment responsivity was examined in a subgroup of participants (n=448). Results:<bold> </bold>Parallel analysis supported the 5-factor structure of the TYDQ. The brief (10-item and 15-item) versions were associated with better model fit than the 21-item version, as revealed by its comparative fit index, root-mean-square error of approximation, and Tucker-Lewis index. Configural, metric, and scalar invariance were supported. The 15-item version explained more variance in the 21-item scores than the 10-item version. Internal consistency was appropriate (eg, the 15-item version had a Cronbach alpha of >0.90 in both samples) and there were no marked differences between how the brief versions correlated with validated measures of depression or anxiety symptoms. The measure was responsive to treatment. Conclusions:<bold> </bold>The 15-item version is appropriate for use as a brief measure of daily actions associated with mental health while balancing brevity and clinical utility. Further research is encouraged to replicate our psychometric evaluation in other settings (eg, face-to-face services).
