OPTION 4

Power Computations for Designing Comparative Poisson Trials with Unequal Group Sizes

Ref: Brown CC, Green SB: Additional power computations for designing comparative Poisson trials. Am J. Epidemiol 1982; 115: 752-8.

This program extends power computations for designing comparative Poisson trials to the situation where the experimental and control populations are of unequal sizes. The computations are valid when testing the one-sided alternative that the incidence rate of a rare disease in one population exceeds that in another population. Calculations are based on an exact test conditional on the combined number of events observed in both populations. The program may also be used to determine sample sizes for comparative binomial trials with very small binomial parameters when the numbers of patients in the two groups are not necessarily equal.

The user must supply the control group incidence rate expressed as the number of events per patient time unit of observation. This number is necessarily small e.g. .001 incidence could mean that in 1000 controls followed for 10 years, we would expect 10 occurrences of the disease. The expected increase in incidence in the experimental population for which power is desired must also be provided; this is indicated as a ratio of incidence rates (experimental/controls). For unequal populations, the user must supply the ratio (experimental/controls) of population sizes along with the one-sided alpha level of the statistical test. The program can then calculate either the two sample sizes, the expected trial duration or the power when provided with the other two.

Option 4.1

Poisson Trials with Unequal Group Sizes, Adjusted for Compliance

Ref: Prorok PC, Andriole GL, Bresalier R, Buys S, Chia D, Crawford ED, Fogel R, Gelmann EP, Gilbert F, Hasson MA, Hayes R, Johnson CC, Mandel JS, OBrien B, Oken M, Rafla S, Reding D, Rutt W, Weissfeld JL, Yokochi L, Gohagan JK. Design of the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. Controlled Clin Trials Suppl 2000;21(6S):273S-309S

This related program includes two additional parameters to allow adjusting for levels of compliance in the screened and control arms.

(P1) Compliance in Screened: (values 0-1) and (P2) Compliance in Controls : (values 0-1)