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Covariance
Explanations > Social Research > Statistical principles > Covariance Description  Example  Discussion  See also
DescriptionDeviation of a variable in a sample is its value minus the sample mean (xbar). dev(x) = x  xbar Covariance is a measure of how much the deviations of a pair of variables match. cov(x,y) = SUM( (x  xbar)*(y  ybar) ) A higher number for covariance indicates strong matching. A negative number indicates weak matching. ExampleIn the first table below, x and y go up and down together. In the second table, they are a lot less similar.
DiscussionThere is no limit to covariance, which makes it difficult to assess given a single calculation. It has more value when several sets of similar figures have their covariances calculated. In this case, the set with the highest figure has the greatest matching. SPSS: Analyze, Correlate, Bivariate; Options: Crossproduct deviations and covariations. See also

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