Year	Number of
1990	4.96
1991	5.11
1992	5.27
1993	5.4
1994	5.53
1995	5.67
1996	5.81
1997	5.96
1998	6.11
1999	6.21
2000	6.28
2001	6.39
2002	6.49
2003	6.6
2004	6.73
2005	6.89
2006	7.04
2007	7.18
2008	7.29
2009	7.44
2010	7.61
2011	7.77
2012	7.95
2013	8.11
2014	8.27
2015	8.42
2016	8.7