Year	Number of
1990	9.8
1991	9.86
1992	9.89
1993	9.91
1994	9.93
1995	9.97
1996	10.31
1997	10.69
1998	11.1
1999	11.5
2000	11.91
2001	12.31
2002	12.7
2003	13.08
2004	13.48
2005	13.96
2006	14
2007	14.06
2008	14.19
2009	14.35
2010	14.54
2011	14.61
2012	14.71
2013	14.8
2014	14.9
2015	14.99
2016	15.12