Year	Number
1996	17.0147
1997	16.69722
1998	17.21601
1999	17.91437
2000	16.82985
2001	17.69108
2002	16.81736
2003	17.13133
2004	16.74773
2005	16.22654
2006	15.71211
2007	15.93711
2008	16.07127
2009	17.3139
2010	17.49009
2011	17.46208
2012	17.41818
2013	17.63101
2014	17.73363
2016	17.61018
2017	15.20744