Affective variability in depression: Revisiting the inertia-instability paradox.

How can depression be associated with both instability and inertia of affect? Koval et al. (2013, Emotion, 13, 1132) showed that this paradox can be solved by accounting for the statistical overlap between measures of affect dynamics. Nevertheless, these measures are still often studied in isolation. The present study is a replication of the Koval et al. study. We used experience sampling data (three times a day, 1 month) of 462 participants from the general population and a subsample thereof (N = 100) selected to reflect a uniform range of depressive symptoms. Dynamics measures were calculated for momentary negative affect scores. When adjusting for the overlap among affect dynamics measures, depression was associated with 'dispersion' (SD) but not 'instability' (RMSSD) or 'inertia' (AR) of negative affect. The association between dispersion and depression became non-significant when mean levels of negative affect were adjusted for. These findings substantiate the evidence that the presumed association between depression and instability is largely accounted for by the SD, while the association between dispersion and depression may largely reflect mean levels of affect. Depression may thus not be related to higher instability per se, which would be in line with theories on the adaptive function of moment-to-moment fluctuations in affect.