Year	Number of
1990	12.49
1991	12.76
1992	13.08
1993	13.27
1994	13.4
1995	13.47
1996	13.62
1997	13.81
1998	14.18
1999	14.19
2000	14.41
2001	14.32
2002	14.38
2003	14.55
2004	14.67
2005	14.98
2006	15.23
2007	15.39
2008	15.67
2009	16.01
2010	16.54
2011	16.89
2012	17.47
2013	17.99
2014	18.68
2015	19.22
2016	19.78