Year	Number of
1990	4.95
1991	5.03
1992	5.11
1993	5.21
1994	5.34
1995	5.46
1996	5.56
1997	5.68
1998	5.76
1999	5.74
2000	5.73
2001	5.66
2002	5.5
2003	5.44
2004	5.31
2005	5.27
2006	5.23
2007	5.14
2008	5.24
2009	5.27
2010	5.36
2011	5.49
2012	5.6
2013	5.71
2014	5.83
2015	5.96
2016	6.09