If a common Kaplan–Meier estimatorS is fitted and the same data are transformed to ui=−logS(xi) with censoring indicators retained, event ordering and risk sets are preserved under compatible tie conventions. At a transformed eventtime uj, the residual product-limit estimate equals S(xj)=e−uj. Consequently agreement of the pooled residual curve with the exponential target is largely built into the construction. Separate groupcurves or amodel fitted with covariates can reveal differences concealed by the pooled fit. Residuals become infinite if the fitted survivor reaches zero.
