© 2001 by Biometrika Trust
Effects attributable to treatment: Inference in experiments and observational studies with a discrete pivot
1 Department of Statistics, The Wharton School of the University of Pennsylvania, Philadelphia, Pennsylvania 19104-6302, U.S.A.e-mail: rosenbaum{at}stat.wharton.upenn.edu
In randomisation and permutation inference, pivotal arguments remove the hypothesised treatment effect, thereby basing inferences on the null distribution in which the treatment has no effect. This is common, for instance, with additive treatment effects. The current paper uses attributable eects» to expand substantially the scope of pivotal arguments.Attributable effects are defined for three cases, namely the 2 x 2 contingency table, displacement eects and the MannWhitneyWilcoxon statistic, and in each case removing an appropriate attributable effect restores the familiar null randomisation distribution of the associated statistic, yielding exact inferences. The procedure extends immediately for use in sensitivity analysis in nonrandomised observational studies.
Key Words: Attributable risk; Control median test; Fisher's exact test; Placement; Randomisation inference; Sensitivity analysis