Year	Number of
1990	3.39
1991	3.52
1992	3.66
1993	3.78
1994	3.91
1995	4.02
1996	4.1
1997	4.19
1998	4.28
1999	4.38
2000	4.5
2001	4.62
2002	4.76
2003	4.91
2004	5.09
2005	5.28
2006	5.48
2007	5.71
2008	5.96
2009	6.23
2010	6.53
2011	6.74
2012	6.97
2013	7.26
2014	7.54
2015	7.82
2016	8.1