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# Covariance and Correlation

Covariance Covariance is just an extension of the idea of variance: instead of looking at how numbers in one data set deviate from their mean, you look at how numbers in two data sets deviate from their respective means together. We start with the formula for variance (of a population): \[\sigma^2\ =\ \frac{\sum_{i=1}^N \left(X_i\ –\ […]