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Clinical trials 

Clinical trials
Chapter:
Clinical trials
Author(s):

Patrick P.J. Phillips

and Andrew J. Nunn

DOI:
10.1093/med/9780198719830.003.0005
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date: 30 November 2020

Randomized controlled trials generate the most reliable evidence for assessing new interventions; while observational studies can provide useful information, they are more likely to be subject to biases. Trials are often separated into four phases, beginning with early safety studies and leading to large-scale trials assessing clinically relevant long-term outcomes. The sample size is a critical decision for every trial that depends upon several assumptions and needs to be adequate to minimize the probability that the results are just chance findings (type I and type II errors). Adaptive trial designs allow for ongoing data to be used to modify aspects of a trial before it is completed. Randomization with allocation concealment and collection of good-quality data free from bias are some of the essential features of a well-conducted trial, together with independent oversight committees monitoring trial conduct and patient safety.

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