A procedure used to test <a href="search.pl?p=predictive validity">predictive validity</a>, typically with <a href="search.pl?p=longitudinal">longitudinal</a><I> </I>or <a href="search.pl?p=cross-sectional data">cross-sectional data</a>. The data to be analyzed are split into two roughly equal subsets. A model is estimated on one subset and its ability to forecast is tested on the other half. The model is then estimated for the other subset, which is then used to forecast for the first subset. This procedure requires a large sample size. (Also see <a href="search.pl?p=jackknife">jackknife</a>.)<o:p></o:p></P>