Thanks for your response, Ben! The paper that argued the use of the identity link with Gamma for response time data is Lo & Andrews (2015) (doi: 10.3389/fpsyg.2015.01171 <https://dx.doi.org/10.3389%2Ffpsyg.2015.01171>). Would such a model still be computationally problematic if the observed values fall very much within the domain of the specified probability distribution (i.e., valid response times are always above 200 ms)? Re: "allow for correlations of random effects to be estimated", I've been told that it's more tractable to estimate covariances between the random slopes and intercepts (as I want with my model) using PQL than Laplace/AGHQ. In fact, Lo & Andrews' demonstration using glmer explicitly specified the covariances between the slopes and the intercepts to be 0 due to the computational rigor of specifying a model with random intercept-slope covariances in glmer and due to theoretical reasons. And thanks for pointing out the Pinheiro & Bates (2000) reference to specifying crossed effects! Sincerely, Van Liceralde
Van Rynald T. Liceralde, BS, BA Graduate Student, Cognitive Psychology University of North Carolina at Chapel Hill [[alternative HTML version deleted]]