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Governed by a formal chance process in which the occurrence of previous events is of no value in predicting future events. For example, the probability of assigning a participant to one of two specified groups which is 50%.
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Related Glossary Terms:
- BiasSystematic deviation from the underlying truth due to a feature of the design or conduct of a research study (for example, overestimation of a treatment effect due to failure to randomize).
- Random ErrorWe can never know with certainty the true value of an intervention effect because of random error. It is inherent in all measurement. The observations that are made in a study are only a sample of all possible observations that could be made from the population of relevant patients. Thus, the average value of any sample of observations is subject to some variation from the true value for that entire population. When the level of random error associated with a measurement is high, the measurement is less precise and we are less certain about the value of that measurement.
- Random-Effects ModelA model used to give a summary estimate of the magnitude of effect in a meta-analysis that assumes that the studies included are a random sample of a population of studies addressing the question posed in the meta-analysis. Each study estimates a different underlying true effect, and the distribution of these effects is assumed to be normal around a mean value. Because a random-effects model takes into account both within-study and between-study variability, the confidence interval around the point estimate is, when there is appreciable variability in results across studies, wider than it could be if a fixed-effects model were used.
- Truncated TrialsTruncated RCTs are trials stopped early because of apparent harm, because the investigators have concluded that they won’t be able to demonstrate a treatment effect (futility), or because of apparent benefit. Believing the treatment from RCTs stopped early for benefit will be misleading if the decision to stop the trial resulted from catching the apparent benefit of treatment at a random high.
- RandomizationAllocation of participants to groups by chance, usually done with the aid of a table of random numbers. Not to be confused with systematic allocation or quasi-randomization (e.g., on even and odd days of the month) or other allocation methods at the discretion of the investigator.