Year	Number of
1990	3.94
1991	4.1
1992	4.29
1993	4.48
1994	4.69
1995	4.91
1996	5.12
1997	5.32
1998	5.54
1999	5.78
2000	6.06
2001	6.3
2002	6.55
2003	6.81
2004	7.01
2005	7.27
2006	7.51
2007	7.75
2008	8.07
2009	8.4
2010	8.73
2011	8.92
2012	9.19
2013	9.41
2014	9.65
2015	9.92
2016	10.2