Intended for healthcare professionals

General Practice

Understanding controlled trials: Why are randomised controlled trials important?

BMJ 1998; 316 doi: (Published 17 January 1998) Cite this as: BMJ 1998;316:201
  1. Bonnie Sibbald, reader in health services researcha,
  2. Martin Roland, director of research and developmenta
  1. aNational Primary Care Research and Development Centre, University of Manchester, Manchester M13 9PL
  1. Correspondence to: Dr Sibbald

    Randomised controlled trials are the most rigorous way of determining whether a cause-effect relation exists between treatment and outcome and for assessing the cost effectiveness of a treatment. They have several important features:

    • Random allocation to intervention groups

    • Patients and trialists should remain unaware of which treatment was given until the study is completed-although such double blind studies are not always feasible or appropriate

    • All intervention groups are treated identically except for the experimental treatment

    • Patients are normally analysed within the group to which they were allocated, irrespective of whether they experienced the intended intervention (intention to treat analysis)

    • The analysis is focused on estimating the size of the difference in predefined outcomes between intervention groups.

    Other study designs, including non-randomised controlled …

    View Full Text