Year	Number of
1990	9.23
1991	9.5
1992	9.8
1993	10.11
1994	10.41
1995	10.73
1996	10.94
1997	11.16
1998	11.32
1999	11.45
2000	11.62
2001	11.81
2002	12.1
2003	12.44
2004	12.81
2005	13.23
2006	13.6
2007	13.95
2008	14.34
2009	14.77
2010	15.23
2011	15.49
2012	15.93
2013	16.33
2014	16.81
2015	17.34
2016	17.89