1. From the Department of Epidemiology and Biostatistics (W.T.M., A.W.H., D.R., M.L.B., A.H., D.E.G.) and the Department of General Practice (W.T.M., D.R.), Erasmus University Medical School, Rotterdam; and the Department of General Practice (A.W.H.), and Julius Center for Patient Oriented Research (A.W.H., M.L.B., D.E.G.), Utrecht University, Utrecht, the Netherlands.