Year	Number of
1990	4.17
1991	4.31
1992	4.47
1993	4.63
1994	4.81
1995	5.01
1996	5.16
1997	5.34
1998	5.53
1999	5.72
2000	5.93
2001	6.14
2002	6.35
2003	6.57
2004	6.81
2005	7.06
2006	7.31
2007	7.57
2008	7.87
2009	8.18
2010	8.5
2011	8.71
2012	8.94
2013	9.2
2014	9.47
2015	9.77
2016	10.09