 From preliminary data queries, we estimate a study population of 160,000 members with bipolar disorder from 2004-2013. Our data include detailed information about insurance type, diagnoses, health services and pharmacy utilization, out-of-pocket payments, individual-level patient characteristics like income, and neighborhood-level factors like racial density. The unprecedented large sample size will allow us to answer questions about how patients from particular vulnerable subgroups respond to HDHPs, including patients who are Black or Hispanic, have low incomes, reside in rural areas, and have major comorbidities. 