Impact of measurement frequency on self-reported depressive symptoms: An experimental study in a clinical setting.

Background: Previous research suggests a relationship between measurement frequency of self-reported depressive symptoms and change in depressive symptom scores for the Beck Depression Inventory-II (BDI-II). The goal of the current study was to investigate the differential effects of weekly and monthly completion of the BDI-II and Quick Inventory of Depressive Symptomatology self-report (QIDS-SR). Methods: Seventy individuals diagnosed with major depressive disorder (MDD) waiting for treatment were randomly assigned to either completing BDI-II weekly, BDI-II monthly, QIDS-SR weekly, or QIDS-SR monthly for a duration of nine weeks. After nine weeks participants also completed the Zung depression scale once. Mixed multilevel regression modelling and Bayesian Statistical Analysis were used to test the relationship between the measurement frequency and depression scores, and to compare scores of the repeatedly completed instruments with the instrument completed only in week nine. Results: Measurement frequency was not related to BDI-II, QIDS-SR or Zung scores. However, depression scores declined in the weekly and monthly QIDS-SR (but not BDI-II) conditions, while Bayesian analyses indicated moderate support for equal depression scores on the Zung SDS. Limitations: Lack of a clinician-rated depression scale at week nine in addition to the self-report measure. Conclusion: In contrast to previous studies in non-clinical samples, our findings suggest that measurement frequency does not have an impact on scores of the BDI-II. Implications for clinical studies monitoring depressive symptom scores with self-report scales are discussed. Keywords: major depressive disorder; retest effects; measurement error; measurement frequency; Beck Depression Inventory; Quick Inventory of Depressive Symptomatolog