Sampling (Statistics)

Updated 17 Sep 2026

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What it is
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  selecting observational units from a Population to obtain a Sample (Statistics)
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Probability sampling
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  simple random — each possible sample of a specified size has equal probability
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  stratified —sample within defined subgroups
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  cluster — select groups, then observe all or a sample of their members
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  systematic — select at regular intervals after an appropriate random start
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Nonprobability sampling
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  convenience — select accessible units
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  purposive — select units for characteristics relevant to the question
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  snowball — participants help identify further participants
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Planning
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  define the target population, accessible population, sampling frame, inclusion/exclusion criteria, and sample-size justification
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  consider selection bias, nonresponse, measurement quality, and dependence—not only sample size
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Example
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  an election quick count estimates results using sampled polling stations; a complete count aims to enumerate all votes
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Distinguish from
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  Unavailable reference — discretizing spatial positions in an image

Linked references 3