Review: rapid cycling bipolar disorder associated with female gender and bipolar type II subgroup.

Study selection and analysis: Eligible studies compared people with rapid cycling (>4 mood episodes/year) and non-rapid cycling bipolar disorder; clearly described selection of participants, diagnostic criteria, stated whether rapid cycling was lifetime or current and assessed 18 potential risk factors (reported by at least three studies) associated with rapid cycling. Studies in that only selected people with rapid cycling were excluded. Mean random effect sizes for potential risk factors were calculated.