Association between median family income and self-reported mood symptoms in bipolar disorder

Objective: There is broad consensus from epidemiologic research that lower socioeconomic status is related to poorer health. This study investigated the relation between median family income and self-reported mood symptoms in patients with bipolar disorder who reside in the United States.

Methods: Two hundred eighty-four patients with bipolar disorder provided daily self-reported mood ratings for 6 months (50,054 days of data). Regardless of income, all patients were treated by a psychiatrist, took psychotropic medications, and participated in computerized self-monitoring throughout the study. Median family income was obtained from US census tract data. The association between income and mood was analyzed using income as both a continuous and categorical variable. Demographic characteristics were compared by income group. Education level was included in the analysis a priori.

Results: Both the continuous and categorical approaches found a positive association between income and euthymia, a negative association between income and manic/hypomanic symptoms including those due to mixed states, and no association between income and depressive symptoms. Patients in the lower-income group spent 12.4% fewer days euthymic than those in the upper-income group and 9.7% fewer days euthymic than those in the middle-income group. Patients in the lower-income group spent 7.1% more days with manic/hypomanic symptoms than those in the upper-income group. There was no association between education and income.

Conclusion: Median family income is associated with mood symptoms in patients with bipolar disorder. Inclusion of income as a measure of socioeconomic status is recommended for future studies of outcome in bipolar disorder.