Small-sample adjustments for Wald-type tests using sandwich estimators

Biometrics. 2001 Dec;57(4):1198-206. doi: 10.1111/j.0006-341x.2001.01198.x.

Abstract

The sandwich estimator of variance may be used to create robust Wald-type tests from estimating equations that are sums of K independent or approximately independent terms. For example, for repeated measures data on K individuals, each term relates to a different individual. These tests applied to a parameter may have greater than nominal size if K is small, or more generally if the parameter to be tested is essentially estimated from a small number of terms in the estimating equation. We offer some practical modifications to these robust Wald-type tests, which asymptotically approach the usual robust Wald-type tests. We show that one of these modifications provides exact coverage for a simple case and examine by simulation the modifications applied to the generalized estimating equations of Liang and Zeger (1986), conditional logistic regression, and the Cox proportional hazard model.

MeSH terms

  • Analysis of Variance*
  • Bias
  • Biometry
  • Humans
  • Logistic Models
  • Models, Statistical*
  • Proportional Hazards Models