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![Pooled, within-group, and between-group covariance matrices](https://blogs.sas.com/content/iml/files/2020/07/pooledCov5-400x336.png)
A previous article discusses the pooled variance for two or groups of univariate data. The pooled variance is often used during a t test of two independent samples. For multivariate data, the analogous concept is the pooled covariance matrix, which is an average of the sample covariance matrices of the