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Please use this identifier to cite or link to this item: http://hdl.handle.net/1942/5877

Title: Group sequential methods for an ordinal logistic random-effects model under misspecification
Authors: Spiessens, B.
LESAFFRE, Emmanuel
Kim, K.M.
Issue Date: 2002
Citation: Biometrics, 58. p. 569-575
Abstract: Interim analyses in clinical trials are planned for ethical as well as economic reasons. General results have been published in the literature that allow the use of standard group sequential methodology if one uses an efficient test statistic, e.g., when Wald-type statistics are used in random-effects models for ordinal longitudinal data. These models often assume that the random effects are normally distributed. However, this is not always the case. We will show that, when the random-effects distribution is misspecified in ordinal regression models, the joint distribution of the test statistics over the different interim analyses is still a multivariate normal distribution, but a sandwich-type correction to the covariance matrix is needed in order to obtain the correct covariance matrix. The independent increment structure is also investigated. A bias in estimation will occur due to the misspecification. However, we will also show that the treatment effect estimate will be unbiased under the null hypothesis, thus maintaining the type I error. Extensive simulations based on a toenail dermatophyte onychomycosis trial are used to illustrate our results.
URI: http://hdl.handle.net/1942/5877
DOI: 10.1111/j.0006-341X.2002.00569.x
ISI #: 000182975800010
ISSN: 0006-341X
Category: A1
Type: Journal Contribution
Appears in Collections: Research publications

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