Year Number 1996 34.32115 1997 33.69607 1998 33.43013 1999 33.83403 2001 35.79195 2002 38.93179 2003 44.31462 2004 44.97935 2005 48.20127 2006 32.44961 2007 30.58316 2008 31.22998 2010 34.56216 2011 37.17552 2012 41.36246 2013 32.74575 2014 26.62827 2015 33.3801 2016 30.52872 2017 34.73504