Year	Number of
1990	7.37
1991	7.68
1992	7.93
1993	8.06
1994	8.14
1995	8.22
1996	8.22
1997	8.12
1998	8.09
1999	8.29
2000	8.5
2001	8.85
2002	9.25
2003	9.79
2004	10.56
2005	11.19
2006	11.84
2007	12.54
2008	13.15
2009	13.84
2010	14.49
2011	15.46
2012	16.61
2013	17.64
2014	18.56
2015	19.43
2016	20.34