Abstract
In many biological problems, the experimenter many prefer to use a chi-square test for linear trends in proportions rather than the standard chi-squared test of homogeneity. In this paper the non-centrality parameter of this test for linear trend in such a model is calculated. This permits the experimenter to make power comparisons between the two tests and some tables are presented along such lines. The power of the test for linearity in the same model is also studied. Such power studies permit determination of sample size and an example is discussed using published data on the possible effect of maternal smoking on the sex ratio at birth.