Year	Number of
1990	6.19
1991	6.39
1992	6.57
1993	6.79
1994	7
1995	7.23
1996	7.44
1997	7.7
1998	8.02
1999	8.39
2000	8.84
2001	9.32
2002	9.84
2003	10.36
2004	10.87
2005	11.37
2006	11.78
2007	12.14
2008	12.45
2009	12.78
2010	13.05
2011	13.27
2012	13.48
2013	13.7
2014	13.97
2015	14.29
2016	14.49