© 1999 by Biometrika Trust
An empirical adjustment to the likelihood ratio statistic
Department of Statistics, Northwestern University, Evanston, IL 60208-4070, USA E-mail: severini@nwu.edu
Consider a model parameterised by a scalar parameter of interest
and a nuisance parameter
. Inference about
may be based on the signed square root of the likelihood ratio statistic, R. The statistic R is asymptotically distributed according to a standard normal distribution, with error O(n-
). To reduce the error of this normal approximation, several modifications to R have been proposed such as Barndorff-Nielsen's modified directed likelihood statistic, R*. In this paper, an approximation to R* is proposed that can be calculated numerically for a wide range of models. This approximation is shown to agree with R* with error of order Op(n-1). The results are illustrated on several examples.
Key Words: ABC interval; Conditional inference; Confidence limits; Directed likelihood-ratio.