Although the first controlled trial in health care is thought
to have occurred at least 3 centuries ago, the modern era of randomized controlled
trials (RCTs) began in the late 1940s with the pioneering work of Bradford
Hill.1 During this 50-year period, RCTs have
made important contributions in health care and have been used extensively.
Hundreds of thousands of RCTs have been published, and the doubling time in
some research areas is less than 10 years.2
The main appeal of the RCT as a research tool in health care derives from
its potential for reducing selection bias, particularly during the evaluation
of diagnostic or therapeutic interventions. Researchers expect that randomization,
if done properly, can keep study groups as similar as possible at the outset,
thus enabling the investigators to isolate and quantify the effect of the
interventions they are studying and control for other factors. No other study
design allows researchers to balance unknown prognostic factors at baseline.
Random allocation, however, does not protect RCTs against other types of bias.
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