Is time of the essence? The impact of different recall periods on participant responses to the depression, anxiety, and stress questionnaire.

There are a significant number of instruments available to measure mental health symptoms, which can limit the comparability and integration of data. Retrospective harmonization facilitates the comparison of data from different sources; however, researchers must test measurement invariance testing before harmonization can be conducted. To date, harmonization research has typically focused on the semantic content of scale items, and limited attention has been given to the recall period (e.g., 1 week and 1 month). Three groups of university students completed the Depression, Anxiety, and Stress Scale (DASS-21) based on their symptoms in the “past week” (n = 134), “past month” (n = 134), and “past 6 months” (n = 127). The latent structure of the DASS-21 was first estimated using confirmatory factor analysis. Then, differential item functioning (DIF) was tested using a moderated mediation multiple indicators multiple cause model with the recall period group as a covariate. Confirmatory factor analysis results supported a three-factor model fit the data. Multiple indicators multiple cause models indicated that none of the DASS-21 items displayed uniform or nonuniform DIF across groups. However, the “6 months” group had significantly higher mean depression scores compared to the “1 week” group. The lack of DIF between groups indicates that the recall period of the DASS-21 did not affect item response. The results suggest that different recall periods may not be a barrier to retrospective harmonization, although further research should identify the mechanisms underlying participant symptom ratings across different recall periods.