Author contributions
R.B.S. and J.L.G. conceived the study; J.L.G., B.J.B., P.J.B., K.L., C.M., A.M., N.J.P., L.J.W. and R.B.S. contributed to data collection; R.B.S., K.L. and P.J.B. set up the PIT project; B.J.B., K.L. and L.J.W collated the databases; K.L. manages the PIT project; R.B.S., K.L. and P.J.B. obtained the funding; F.L. analysed the data and made the figures, with help and guidance from J.L.G. and R.B.S.; F.L. wrote the first draft of the manuscript; all authors contributed to revisions and gave final approval for publication.