Year	Number of
1990	8.84
1991	9.4
1992	9.7
1993	9.69
1994	10.02
1995	10.73
1996	10.41
1997	10.69
1998	10.39
1999	10.09
2000	10.36
2001	10.34
2002	10.54
2003	11.06
2004	11.4
2005	11.78
2006	12.46
2007	12.95
2008	13.37
2009	13.92
2010	14.63
2011	15.17
2012	15.61
2013	15.97
2014	16.39
2015	16.85
2016	16.69