On lachin'S formulae for sample sizes of survival tests
- 1 January 1991
- journal article
- research article
- Published by Taylor & Francis in Communications in Statistics - Theory and Methods
- Vol. 20 (7) , 2267-2280
- https://doi.org/10.1080/03610929108830629
Abstract
Lachin [1981] and Lachin and Foulkes [1986] consider two groups of identically independently exponentially distributed random variables and four models of data sampling. The test problem they treat is to decide whether the two distributions are identical (null-hypothesis H0) or not (alternative hypothesis H1). Basing the test on maximum-likelihood estimators and their asymptotic normal densities they obtain formulae for the group sizes necessary to yield asymptotic tests with guaranteed power under a prescribed level for specified hypotheses. It is intuitively reasonable to expect the sizes decrease the more the hypotheses differ. It the distance betwen H0 and H1 is measured by the difference of the exponential parameters this assumption time or the deviation of the exponential parameter ratio from unity is the measure larger distances between the hypotheses do not necessarily lead to smaller sample sizes.Keywords
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