Intended for healthcare professionals

Endgames Statistical Question

Random sampling versus random allocation

BMJ 2011; 343 doi: (Published 23 November 2011) Cite this as: BMJ 2011;343:d7453
  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 the effects of providing people with evidence based information about colorectal cancer and screening. A randomised controlled study design was used. The intervention was a brochure that included personalised risk of colorectal cancer, available screening options with possible benefits and harm, plus information on prevention of colorectal cancer. People also had access to two optional interactive internet modules on risk and diagnostic tests. The control treatment was the official information leaflet of the German colorectal cancer screening programme. Primary outcome measures included “informed choice” based on knowledge and attitude, plus the planned and actual uptake of screening.1

Potential trial participants were people insured by a large German statutory health insurance scheme who were aged 50-75 years and had no history of colorectal cancer. A total of 7946 people were eligible. A random sample of about 4000 people was drawn and invited to participate in the trial. In total, 1577 agreed and were randomly allocated to the intervention (n=785) or control (n=792).

The researchers …

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