Year	Number of
1990	7.22
1991	7.27
1992	7.39
1993	7.56
1994	7.81
1995	8.19
1996	8.47
1997	8.77
1998	8.93
1999	9.07
2000	9.24
2001	9.45
2002	9.7
2003	10.02
2004	10.32
2005	10.57
2006	10.78
2007	10.96
2008	11.21
2009	11.46
2010	11.71
2011	12.05
2012	12.69
2013	13.11
2014	13.6
2015	14.15
2016	14.74