Adults in the lowest-income group were five times as likely to have signs of depression as were those in the highest-income group. But they were also less likely to receive treatment.

Among the people who received treatment for depression, only 30 percent had screened positive for depression and 22 percent had serious psychological distress. (Patients with serious psychological distress have more-severe symptoms of depression than do those with mild depression, and the condition typically requires treatment beyond antidepressants.) Those with either less serious or no depression were more likely than those with signs of depression to receive antidepressants. That’s a problem of overprescription, Olfson said, because studies have shown that anti­depressants are no more effective for mild depression than a placebo.

“Being a little less aggressive in medication in mild depression would be beneficial,” he said. “There are simpler forms of psychological interventions that can be adapted for primary care.” For example, patients can be given counseling, exercise and yoga.