Intended for healthcare professionals

Endgames Statistical Question

Observational study designs

BMJ 2012; 344 doi: (Published 21 June 2012) Cite this as: BMJ 2012;344:e4209
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
  1. p.sedgwick{at}

Researchers investigated whether pioglitazone was associated with an increased risk of bladder cancer in people with type 2 diabetes.1 Use of pioglitazone, an oral antidiabetic agent in the thiazolidinedione class, is controversial.2 The researchers used the general practice research database to extract data from individual patients’ primary care records between 1988 and 2009. A cohort of 115 727 patients with type 2 diabetes was established, with patients entering the cohort if they had been newly treated with oral hypoglycaemic agents. Patients were considered to have been exposed to pioglitazone if they had ever taken it, and measures of duration of use and cumulative dosage were recorded.

In the cohort 376 cases of bladder cancer were diagnosed. Patients were considered to be a case if their cancer was diagnosed at least one year after entry to the cohort, to account for latency. Each case was matched to as many as 20 controls on year of birth, year of cohort entry, sex, and duration of follow-up. A total of 6699 controls were identified. The researchers reported that the use of pioglitazone was associated with an increased risk of bladder cancer among people with type 2 diabetes. …

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