Year	Number of
1990	11.76
1991	12.29
1992	12.69
1993	13.04
1994	13.45
1995	13.85
1996	14.23
1997	14.58
1998	14.94
1999	15.04
2000	15.12
2001	15.22
2002	15.46
2003	15.78
2004	16.08
2005	16.44
2006	16.77
2007	17.21
2008	17.63
2009	17.98
2010	18.28
2011	18.55
2012	18.81
2013	19
2014	19.08
2015	19.36
2016	19.67