This article was originally published containing three figures (Figures 8-10) and seven tables (Tables 6-13) intended solely for Supplementary Materials (Zeller supplementary material 1). These objects have been removed from the main article and are visible in Zeller supplementary material 1. The publisher apologises to the author for this error.
A formatting error in a reference in footnote 14 has been corrected to read Beck and Miner (2013).