= Extra sum of squares
{title2=$SS_{\rm extra}=RSS_{\rm reduced}-RSS_{\rm full}$}
For nested <normal linear models>, the decrease in <residual sum of squares> obtained by adding coefficients is their extra sum of squares. Dividing by the number of added coefficients and by the full-model residual mean square gives the partial <F-test>. A sequential <analysis of variance> attributes this decrease according to the specified order of entry; it need not equal the partial comparison when other terms are retained.
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