I'm looking for any papers that compare properties of asymptotic tests (wald, likelihood ratio) with properties of approximate F-tests in linear mixed models. I'm particularly interested in tests of linear combinations of fixed effects parameters, but tests of any type of hypothesis will do. An article with simulation studies in which power, size, etc. are estimated and compared would be perfect. I'm working on a paper for a class and I'm having trouble locating an article covering this topic (I know they're out there). I have access to many online journals through my university, so any suggested articles would be greatly appreciated!