Year	Number of
1990	8.23
1991	8.4
1992	8.55
1993	8.71
1994	8.87
1995	9.04
1996	9.21
1997	9.4
1998	9.53
1999	9.65
2000	9.73
2001	9.68
2002	9.72
2003	9.81
2004	9.89
2005	9.87
2006	10.04
2007	10.31
2008	10.65
2009	11.18
2010	11.89
2011	12.51
2012	13.09
2013	13.99
2014	14.67
2015	15.55
2016	16.36