Statistical Question

Stratified random allocation

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f822 (Published 8 February 2013)
Cite this as: BMJ 2013;346:f822

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  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 effects of manual lymph drainage on the development of lymphoedema related to breast cancer. A randomised single blinded controlled trial was performed. The intervention was a six months’ treatment programme consisting of guidelines about prevention of lymphoedema, exercise therapy, and manual lymph drainage. Control treatment consisted of the same programme as the intervention but without manual lymph drainage.1

Participants were consecutive patients with breast cancer and unilateral axillary lymph node dissection. Randomisation to treatment groups occurred in a 1:1 ratio using stratification by body mass index (≤25 or >25) and postoperative axillary irradiation (yes or no). Allocation was achieved using random permuted blocks of size four. In total, 160 patients were recruited, with 79 allocated to the intervention and 81 allocated to control.

The main outcome measures were incidence of arm lymphoedema and time until development of arm lymphoedema. One year after surgery, there was no significant difference between treatment groups in the cumulative incidence rate for arm lymphoedema and the time to development of arm lymphoedema.

Which of the following …

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