Year	Number of
1990	9.08
1991	9.34
1992	9.64
1993	9.94
1994	10.21
1995	10.51
1996	10.8
1997	11.13
1998	11.44
1999	11.59
2000	11.56
2001	11.55
2002	11.7
2003	12.08
2004	12.36
2005	12.78
2006	13.38
2007	13.88
2008	14.3
2009	14.56
2010	14.67
2011	14.88
2012	15.11
2013	15.87
2014	16.6
2015	17.31
2016	18