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

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.

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.

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.

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.