Year	Number of
1990	9.8
1991	10.52
1992	11.09
1993	11.9
1994	12.5
1995	11.95
1996	11.69
1997	11.53
1998	11.37
1999	11.15
2000	10.96
2001	10.81
2002	10.77
2003	11.06
2004	12.06
2005	12.41
2006	12.79
2007	13.18
2008	13.68
2009	14.29
2010	14.6
2011	14.9
2012	15.19
2013	15.44
2014	15.7
2015	15.95
2016	15.97