Year	Number of
1990	9.7
1991	10.06
1992	10.36
1993	10.62
1994	10.9
1995	11.18
1996	11.44
1997	11.7
1998	11.97
1999	12.14
2000	12.31
2001	12.47
2002	12.69
2003	12.96
2004	13.23
2005	13.49
2006	13.74
2007	13.97
2008	14.2
2009	14.42
2010	14.62
2011	14.77
2012	14.9
2013	15.03
2014	15.09
2015	15.27
2016	15.5