Bias in the one-step method for pooling study results.

The one-step (Peto) method for obtaining pooled effect estimates can yield extremely biased results when applied to unbalanced data. Even for balanced studies, the one-step estimate may incorporate an unacceptable degree of bias. In place of the one-step estimate, we recommend use of ordinary Mantel-Haenszel, weighted least squares, or maximum likelihood estimates whenever the total number of events is adequate for such methods. If the total number of events is small, we recommend exact methods.