Most people who commit suicide suffer from depression, but diagnostic categories and known personal and demographic factors do not adequately capture the distress that leads people to kill themselves. Mood Instability (MI) refers to sudden unpredictable fluctuations in mood often occurring within a day.

To determine whether MI predicts suicidal thoughts.

Hypothesis: That MI will predict suicidal thoughts even when negative affect (depression, anxiety, anger) are controlled.

Data from the Dutch Imigrant panel of the Longitudinal Internet Studies for the Social Sciences (LISS-I) (N = 1686) were used. MI was assessed with 7 items from the International Personality Item Pool of Big Five Indicators. The Chronbach's alpha was 0.86. Suicidal thoughts were assessed by a single question referring to the past week. Depression, anxiety and anger were represented by 21 items derived by factor analysis from the 31-item Emotional Expressiveness Module. Odds ratios using logistic regression modeling were calculated, adjusting for negative affect, alcohol and substance abuse, and demographic variables (age, sex, income).

MI predicts suicidal thoughts (Males OR: 1.14; 95% CI: 1.02-1.28 and females OR: 1.11; 95% CI: 1.00-1.23) along with negative affect. There was no interaction between MI and negative affect.

MI has been relatively neglected as a predictor of suicidal thoughts. It is likely that the unpredictable, sudden, severe descents in mood are particularly distressing and contribute to the feeling that life is intolerable. MI requires more attention in the assessment and treatment of suicide risk.