Year	Number of
1990	7.32
1991	7.34
1992	7.38
1993	7.33
1994	7.3
1995	7.3
1996	7.53
1997	7.83
1998	8.17
1999	8.52
2000	8.88
2001	9.25
2002	9.57
2003	9.9
2004	10.31
2005	10.57
2006	10.9
2007	11.18
2008	11.54
2009	11.82
2010	12.03
2011	12.42
2012	13
2013	13.49
2014	14
2015	14.49
2016	15.02