PRESS Statistic

The PRESS statistic is often used in regression analyses, in order to summarize the fit of a particular model in a sample of observations that were not used to estimate the model parameters. It can simply be computed as the sums of squares of the prediction residuals for those observations.
See Draper and Smith (1981); the PRESS statistic is, for example, computed in the Partial Least Squares Model for the cross-validation (verification) samples.