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Understanding controlled trials: Why are randomised controlled trials important?

By Sibbald, B. and M. Roland.


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…

Sibbald, B. and M. Roland (1998). “Understanding controlled trials: Why are randomised controlled trials important?” Bmj 316(7126): 201.