  We provide a generalized revealed preference test for quasilinear
preferences. The test applies to nonlinear budget sets and non-convex
preferences as those found in taxation and nonlinear pricing contexts. We study
the prevalence of quasilinear preferences in a laboratory real-effort task
experiment with nonlinear wages. The experiment demonstrates the empirical
relevance of our test. We find support for either convex (non-separable)
preferences or quasilinear preferences but weak support for the hypothesis of
both quasilinear and convex preferences.
