X.Z. and V.W. did most of the analyses, with the remainder being done by J. Grove, Y.G., C.K.B. and L.K.N. M.K., E. Verhoef, A. Gui, L.H., A.H., A.R., B.S.P. and A.D.B. provided summary statistics for various analyses. V.W. supervised the analyses and directed the study with input from H.C.M. and J. Grove V.W. and X.Z. wrote the initial draft with input from H.C.M. A. Gui, S.A.S.N., A.H., B.S.P., A.R., D.S.M., E.M.W., D.H.G., N.R.W., E.B.R., T.B. and S.B.-C. provided intellectual input. All authors read and commented on the final manuscript.