The validity of daily patient-reported anxiety measured using smartphones and the association with stress, quality of life and functioning in patients with bipolar disorder.

•Patients with bipolar disorder (BD) experience anxiety at that influences their daily living.•Patients with BD used a smartphone-based monitoring system daily for nine months.•Patients evaluated severity of anxiety symptoms validly.•During full or partly in remission symptoms of anxiety was associated with increased stress, decreased quality of life and functioning.•The findings emphasize the importance of identifying anxiety pointing toward smartphones as a valid tool.