Review articleMeta-analysis of the changes in correlations between depression instruments used in longitudinal studies

- Correlations between depression scales increased over time.
- An increase in correlations was associated with a decrease in depression scores.
- An increase in correlations was associated with an increase in depression score variability.
- Different times of observations require different thresholds for acceptable concurrent validity.

BackgroundCorrelations between instruments measuring the same construct reflect their concurrent validity. Little is known about changes in correlations between such instruments employed in studies with repeated assessment. The aim of this meta-analysis was to examine the changes in correlations between depression instruments in the course of longitudinal studies.MethodsA literature search was conducted using MEDLINE and PsycINFO for the period from 1960 to 2013. The total number of collected articles was 3723, of which 61 were included. Three meta-analyses were performed for the changes in correlations between each pair of the three depression scales: Hamilton Rating Scale for Depression (HAMD), Montgomery-Asberg Depression Rating Scale (MADRS) and Beck Depression Inventory (BDI). The effect size in these meta-analyses was obtained by the z-transformation of correlation coefficients.ResultsCorrelations between depression scales increased over time in 52 studies. Significant changes in correlation coefficients were found for correlations between HAMD and BDI (p<0.001) and for correlations between HAMD and MADRS (p<0.001). An increase in correlations between the scales was associated with a decrease in depression scores and increase in their variability.LimitationsUnivariable and multivariable meta-regression models were not obtained in all three meta-analyses because of the lack of data.ConclusionsA finding that correlations between depression instruments tended to increase over time has significant implications for assessment of the concurrent validity of these instruments. In longitudinal designs it is important to estimate correlations between depression scales over time because different thresholds for scale correlations indicate acceptable concurrent validity at different times.