Year	Number of
1990	11.17
1991	11.29
1992	11.41
1993	11.54
1994	11.68
1995	11.83
1996	11.98
1997	12.2
1998	12.49
1999	12.78
2000	13.22
2001	13.8
2002	14.44
2003	15.11
2004	15.76
2005	16.38
2006	16.88
2007	17.33
2008	17.73
2009	18.18
2010	18.55
2011	18.71
2012	18.93
2013	19.15
2014	19.42
2015	19.74
2016	20.05