The primary outcome was an incident diagnosis with bladder cancer, after the index date. Follow-up started on the index date and ended with the first of the following censoring events: incident diagnosis of bladder cancer; transfer out of THIN practice; death; or end of available data. The latter date was taken as 31 August 2010 to minimize the chance of surveillance bias given the U.S. Food and Drug Administration warnings of a possible association between TZDs and bladder cancer in September 2010 (28).