An alternative purging method: controlling the composition-dependent interaction in an analysis of rates.

The purging method controlling for the composition-group interaction developed by Clogg and his associates has proven useful in demographic research. This article proposes an alternative method, partial CD purging, that controls the interaction between composition and the dependent variable. The purged rates from this new method are invariant to changes in the marginal distribution of composition, but those from the earlier purging method are not. Mathematical relationships between the proposed method and other techniques are also explored.