Endgames Statistical Question

Sham treatments

BMJ 2013; 347 doi: https://doi.org/10.1136/bmj.f5819 (Published 27 September 2013) Cite this as: BMJ 2013;347:f5819
  1. Philip Sedgwick, reader in medical statistics and medical education,
  2. Carwyn Hooper, lecturer in medical ethics and law
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}sgul.ac.uk

Researchers assessed the effects of continuous positive airway pressure on blood pressure in patients with moderate to severe obstructive sleep apnoea and recently diagnosed but untreated systemic hypertension. Blood pressure was measured using 24 hour ambulatory monitoring. A randomised double blind placebo controlled trial study design was used. The intervention was optimal therapeutic continuous positive airway pressure. Control treatment was sham continuous positive airway pressure delivered at a very low pressure. In total, 169 patients were assigned to continuous positive airway pressure and 171 to control treatment.1

The primary outcome was mean 24 hour ambulatory blood pressure. For each patient the change at three months from baseline in the primary outcome was recorded. Statistical analysis was undertaken by the principle of intention to treat. When compared with sham continuous positive airway pressure, the within group change at three months in mean 24 hour ambulatory blood pressure of the continuous positive airway pressure group decreased by 1.5 mm Hg (95% confidence interval 0.4 to 2.7; P=0.01). It was concluded that continuous positive airway pressure was associated with a significant …

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