Level and instability of day-to-day psychological well-being and risk for depression.

For 21 days, 123 undergraduates provided measures of their self-esteem, anxiety, causal uncertainty, perceived control over outcomes, and the three constructs comprising A. T. Beck's (1972) cognitive triad. Factor analyses of measures of the mean level and day-to-day instability of these constructs produced 2 factors, level of well-being and day-to-day instability of well-being. Participants also provided 4 measures of risk for depression over 2 1/2 months. For participants who were not at risk for depression, level of day-to-day well-being was negatively related to risk for depression, and this effect was not moderated by day-to-day instability. In contrast, for participants who were classified as at-risk for depression, day-to-day instability of well-being moderated the strength of the negative relationship between level of well-being and risk for depression. The relationship between level of well-being and depression was stronger for participants who were more unstable.