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In studies, random means according to chance, unpredictable, without pattern.
Random processes are used in two ways in studies, and this sometimes causes confusion. In studies of treatment effects, random allocation is used to ensure that treatment comparison groups are similar, so that like is compared with like and the risk of allocation bias is minimized.
In other studies, for example, studies of the prevalence of a health condition, random selection from the population of interest is used to select a sample for a study. This is done to ensure that the participants in the study are representative of the population, and that the results of the study are applicable to the target population.
In everyday language, random sometimes has a different meaning: out of control, unexpected, incongruous, or arbitrary.
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