Inference in generalized linear models with robustness to misspecified variances

Generalized linear models usually assume a common dispersion parameter. This assumption is seldom true in practice, and may cause appreciable loss of type I error control if standard parametric methods are used. We present an alternative semi-parametric group invariance method based on sign flipping of score contributions. Our method requires only the correct specification of the mean model, but is robust against any misspecification of the variance. The method is available in the R library flipscores.