Year	Number of
1990	8.86
1991	9.45
1992	9.77
1993	9.8
1994	10.21
1995	11.03
1996	10.69
1997	10.96
1998	10.64
1999	10.33
2000	10.71
2001	10.58
2002	10.76
2003	11.3
2004	11.63
2005	12
2006	12.68
2007	13.22
2008	13.65
2009	14.2
2010	14.95
2011	15.57
2012	16.03
2013	16.38
2014	16.81
2015	17.27
2016	17.01