The pooled variance estimates the population variance (σ2) by aggregating the variances obtained from two or more samples. The pooled variance is widely used in statistical procedures where different samples from one population or samples from different populations provide estimates of the same variance. This entry explains pooled variance, illustrates its calculation and application, and provides cautionary remarks regarding its use.

Estimate of Population Variance: One Sample Case

In usual research settings, researchers do not know the exact population variance. When there is only one sample from a population, researchers generally use the variance of the sample as an estimate of the population variance. In the case of one sample, the fomula to calculate the sample variance is

where Xis are the observed scores in the sample, n ...

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