Year	Number of
1990	10.82
1991	11
1992	11.18
1993	11.33
1994	11.43
1995	11.57
1996	11.99
1997	12.42
1998	12.78
1999	13.28
2000	13.79
2001	14.05
2002	14.38
2003	14.67
2004	14.98
2005	15.21
2006	15.31
2007	15.46
2008	15.69
2009	15.94
2010	16.02
2011	16.08
2012	16.28
2013	16.49
2014	16.71
2015	16.87
2016	17.06