Intraindividual Fluctuation in Optimism Under Daily Life Circumstances: A Longitudinal Study

Optimism is typically conceptualized as a relatively static tendency regarding positive expectations about one’s future. However, recent studies suggest that optimism may meaningfully fluctuate within individuals over time. To date, little is known about the characteristics of such state optimism and potential cultural difference in state optimism. Accordingly, we developed a Japanese version of the State Optimism Measure (J-SOM) and examined its validity and the nature of intraindividual state optimism fluctuations; we also examined relationships between the J-SOM and other measures of mental health, including trait optimism. We conducted two online longitudinal surveys with different time intervals (weekly, n = 97; monthly, n = 99) targeting university students. Results were largely consistent between the two surveys. We confirmed high factor validity and internal consistency of the J-SOM. The J-SOM showed significant correlations in expected directions with other measures such as depressive mood and subjective happiness. In addition, intraindividual changes in the J-SOM were associated with changes in mood and quality of daily life. Importantly, these associations between intraindividual change in optimism and in other variables were minimal for trait optimism. We also found that state optimism, compared with trait optimism, tended to show larger intraindividual changes over 1, 2, 3, 4, and 8 weeks. In summary, this study developed a translated version of the SOM and validated it, and then showed, for the first time, that state optimism can fluctuate within individuals in daily life over a span of several weeks.