Year	Number of
1990	4.16
1991	4.22
1992	4.31
1993	4.42
1994	4.55
1995	4.7
1996	4.71
1997	4.78
1998	4.94
1999	5.21
2000	5.52
2001	5.46
2002	5.46
2003	5.53
2004	5.54
2005	5.64
2006	5.7
2007	5.65
2008	5.71
2009	5.86
2010	5.93
2011	6.01
2012	6.23
2013	6.55
2014	6.91
2015	7.19
2016	7.29