In the collection of data to study a population of interest there could be said to be two main methods of sampling - probability sampling and nonprobability sampling.
It is usual for experiments to use probability sampling as opposed to nonprobability sampling as probability sampling is best scientific practice (or gold standard).
With probability sampling, in the simplest case, every member or unit of the population of interest (or the target population) has an equal chance of being selected for the study. For more complicated study designs, some stratification might occur so that there is proportional representation of certain groups, for example age-sex bands or socio-economic strata. However, within those defined groups, whose size mirror the proportion of the strata in the target population, members still have an equal chance of being selected for the study. The sampling...
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