Data - Covariance
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Data must be in numeric columns of equal length.

Minitab omits missing data from calculations using a method that is often called pairwise deletion. Minitab omits from the calculations for each column pair only those rows that contain a missing value for that pair.

If you are calculating covariances between multiple columns at the same time, pairwise deletion may result in different observations being included in the various covariances. Although this method is the best for each individual covariance, the covariance matrix as a whole may not be well behaved (for example, it may not be positive definite).