Year	Number of
1990	4.23
1991	4.32
1992	4.43
1993	4.56
1994	4.7
1995	4.87
1996	4.97
1997	5.08
1998	5.24
1999	5.3
2000	5.11
2001	5.16
2002	5.49
2003	5.82
2004	6.19
2005	6.5
2006	6.75
2007	6.97
2008	7.25
2009	7.6
2010	7.89
2011	8.3
2012	8.71
2013	9.12
2014	9.51
2015	9.9
2016	10.18