Endgames Statistical Question

Observational study design

BMJ 2012; 345 doi: https://doi.org/10.1136/bmj.e5856 (Published 05 September 2012) Cite this as: BMJ 2012;345:e5856
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
  1. p.sedgwick{at}sgul.ac.uk

Researchers investigated the effect of the dose of levothyroxine on the risk of fractures in older adults.1 A cohort was identified retrospectively from population health databases for Ontario, Canada. Men and women were included if they were aged over 70 years and had been prescribed replacement levothyroxine treatment for hypothyroidism for the first time between 1 April 2002 and 31 March 2007. The cohort comprised 213 511 prevalent users of levothyroxine. The records of the cohort members were examined until 31 March 2008, and the occurrence of any fracture after the prescription of replacement levothyroxine treatment was recorded. Fracture was defined as the first visit to an emergency department or admission to hospital for any fracture of the wrist or forearm; shoulder or upper arm; thoracic spine, lumbar spine, or pelvis; hip or femur; or lower leg or ankle.

During follow-up, 22 236 cases of hip fracture were recorded in the cohort. For each case of hip fracture five controls were identified, with cases and controls matched for age (within 1 year), sex, and duration in cohort (within 30 days of follow-up). …

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