Year	Number of
1990	4.15
1991	4.44
1992	4.62
1993	4.77
1994	4.94
1995	5.08
1996	5.15
1997	5.2
1998	5.16
1999	5.37
2000	5.46
2001	5.45
2002	5.43
2003	5.42
2004	5.45
2005	5.46
2006	5.43
2007	5.4
2008	5.33
2009	5.31
2010	5.33
2011	5.39
2012	5.42
2013	5.46
2014	5.51
2015	5.59
2016	5.66