Abstract
The Cochran-Armitage test for trends or thresholds in proportions. Young, S. S. (1985) Society for Risk Analysis, 1985 Annual Meeting. the Cochran-Armitage (C-A) test (1954, 1955) is widely used as a test for linear trends in proportions in the analysis of long term rodent studies. Implicit in the use of this test is the assumption that the dose response pattern is known. Although in practice the dose response pattern is often assumed linear on a log dose scale, this test can be used to test for nonlinear dose response patterns. The effect of the choice of different dose response patterns is examined using hypothetical and actual examples of tumor data in rodents. The choice of a particular dose response pattern can greatly influence the p-value from the C-A test. As an alternative to the usual C-A test, a sequential testing procedure, similar to the Williams-t (Williams, 1971, 1972), is suggested. Under the assumption of a threshold model, this procedure gives improved testing and estimation and leads to better inferences.
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