Year	Number of
1990	7.16
1991	7.24
1992	7.38
1993	7.57
1994	7.9
1995	8.38
1996	8.78
1997	9.11
1998	9.28
1999	9.4
2000	9.59
2001	9.84
2002	10.13
2003	10.52
2004	10.88
2005	11.19
2006	11.45
2007	11.67
2008	11.98
2009	12.3
2010	12.65
2011	13.01
2012	13.77
2013	14.2
2014	14.74
2015	15.33
2016	15.98