Simple Random Sample
A simple random sample is a fundamental sampling design.
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Description
For a simple random sample, the probability of selection is equal across all cases.
Most commonly, samples are taken without replacement, which is to say that a selected case cannot be reselected. For a SRS without replacement (SRSWOR), the probability of selection is given by:
where N is the total count of cases, s is the sample, and n(s) is the sample size. In contexts where the sample size is a constant, it's often shortened to n.
A SRS with replacement (SRSWR) means that cases can be selected repeatedly. This requires the introduction of a 'distinct' case function, d(s), such that a summation over the sample is expressed as Σi ∈ d(s). The probability of selection is given by:
