Year	Number of
1990	5.19
1991	5.37
1992	5.54
1993	5.69
1994	5.85
1995	6
1996	6.15
1997	6.31
1998	6.42
1999	6.57
2000	6.71
2001	6.82
2002	6.94
2003	7.06
2004	7.2
2005	7.35
2006	7.54
2007	7.75
2008	8.03
2009	8.36
2010	8.73
2011	8.99
2012	9.27
2013	9.62
2014	10
2015	10.41
2016	10.92