Year	Number of
1990	8.15
1991	8.14
1992	8.21
1993	8.55
1994	8.76
1995	9.05
1996	9.25
1997	9.44
1998	9.66
1999	9.83
2000	10.18
2001	10.57
2002	10.92
2003	11.29
2004	11.48
2005	11.7
2006	11.87
2007	12.18
2008	12.35
2009	12.53
2010	12.97
2011	13.26
2012	13.8
2013	13.95
2014	14.3
2015	14.58
2016	14.45