In
sampling theory, the sampling fraction is the ratio of
sample size to
population
Population is a set of humans or other organisms in a given region or area. Governments conduct a census to quantify the resident population size within a given jurisdiction. The term is also applied to non-human animals, microorganisms, and pl ...
size or, in the context of
stratified sampling, the ratio of the sample size to the size of the stratum.
The formula for the sampling fraction is
:
where ''n'' is the sample size and ''N'' is the population size. A sampling fraction value close to 1 will occur if the sample size is relatively close to the population size. When sampling from a
finite population without replacement, this may cause
dependence between individual samples. To correct for this dependence when calculating the sample
variance
In probability theory and statistics, variance is the expected value of the squared deviation from the mean of a random variable. The standard deviation (SD) is obtained as the square root of the variance. Variance is a measure of dispersion ...
, a
finite population correction (or finite population multiplier) of (N-n)/(N-1) may be used. If the sampling fraction is small, less than 0.05, then the sample variance is not appreciably affected by dependence, and the finite population correction may be ignored.
References
Sampling (statistics)
Statistical ratios
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