Year	Number of
1990	5.16
1991	5.44
1992	5.73
1993	6.04
1994	6.33
1995	6.53
1996	6.67
1997	6.78
1998	6.83
1999	6.8
2000	6.86
2001	7.05
2002	7.43
2003	7.91
2004	8.19
2005	8.33
2006	8.78
2007	9.29
2008	9.97
2009	10.66
2010	11.46
2011	11.81
2012	12.2
2013	12.52
2014	12.93
2015	13.37
2016	13.65