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Résumé :
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The negative binomial family of distributions is indexed by two parameters, m, the mean, and k, where 1/k is a measure of aggregation. In constructing sequential probability ratio tests (SPRTs) concerning m, it has been found necessary to assume a common value of k for the null and alternative hypotheses. A method is shown of assessing the performance of SPRTs without making this assumption, using a model of the dependence of Ic on m. Truncation of the tests is also allowed for. A test can be adjusted to have given error probabilities under the assumptions of varying k and truncation. The power and average sample number of a test are calculated. The method is illustrated by performing sequential hypothesis tests concerning infestation by grass-grub larvae. The accuracy of Wald's approximations for constructing tests having given error probabilities is assessed and found to be low.
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