Year	Number of
1990	5.53
1991	5.6
1992	5.69
1993	5.76
1994	5.85
1995	5.96
1996	5.99
1997	6.01
1998	6.02
1999	6.11
2000	6.13
2001	6.2
2002	6.25
2003	6.31
2004	6.38
2005	6.36
2006	6.33
2007	6.35
2008	6.38
2009	6.39
2010	6.4
2011	6.4
2012	6.4
2013	6.38
2014	6.35
2015	6.34
2016	6.36