The relationship between mood instability and depression: implications for studying and treating depression

Most individuals with depressed mood report mood fluctuations (Mood Instability) within hours or days. This is not recognized in diagnostic criteria or standard rating scales for depression.

That mood instability is a distinct component of the development of depression that has been omitted from criteria for depression because of reliance on retrospective recall and structured interviews. The inclusion of Mood Instability would enhance research into causes and treatment of depression.

We examined three datasets that used retrospective and prospective measures of depressed symptom ratings and mood instability to determine the relationship between the two. Study 1 used data from the 1991 UK Health and Lifestyle Surveys (HALS). Studies 2 and 3 used clinical samples. The scales used to assess mood instability were the mood instability factor from the Eysenck Personality Inventory Neuroticism Scale, the Affective Lability Scale (ALS), and the Visual Analogue Depression Scale (VAS). The depression scales (depressive symptoms) were the General Health Questionnaire (GHQ) depression factor, the Beck Depression Inventory IA (BDI) and the mean from the Visual Analogue Depression Scale (VAS). We used partial correlation analysis to assess the association between mood instability and depression and exploratory factor analysis to determine the factor structure of items pooled from the mood instability and depression scales from studies 1 and 2.

Mood Instability was found to be moderately associated with depressive symptoms. The Pearson's r-values ranged from 0.49 to 0.57. The correlation was lower when recalling mood in the past. The factor analytic solution supported the hypothesis that MI and depressive symptoms are related but distinct constructs.

Reliance exclusively on the retrospective assessment of depressive symptoms has occluded the widespread occurrence of mood instability. Including Mood Instability in diagnostic and assessment criteria would enhance causal and treatment research in depression.