This publication is supported by multiple datasets.  The data used to produce Figures 3, 4, 8 and 10 are available from the University of Bath data archive at http://dx.doi.org/10.15125/BATH-00124  Remaining data was obtained upon request and is available to SWEEG members at http://www.ex.ac.uk/cee/internal/internal/888.doc  The sources of existing data cited in the text are listed in the references section.