Year	Number of
1990	13.05
1991	13.34
1992	13.69
1993	14.04
1994	14.33
1995	14.53
1996	15.06
1997	15.41
1998	15.47
1999	15.48
2000	15.8
2001	15.65
2002	15.78
2003	15.73
2004	16.09
2005	15.96
2006	16.21
2007	16.37
2008	16.32
2009	16.75
2010	17.23
2011	17.44
2012	18.11
2013	18.32
2014	18.77
2015	19.23
2016	19.71