Year	Number of
1990	5.7
1991	5.7
1992	5.72
1993	5.77
1994	5.65
1995	5.77
1996	5.97
1997	6.13
1998	6.4
1999	6.42
2000	6.43
2001	6.49
2002	6.52
2003	6.54
2004	6.54
2005	6.54
2006	6.53
2007	6.33
2008	6.32
2009	6.38
2010	6.27
2011	6.32
2012	6.72
2013	6.62
2014	6.61
2015	6.62
2016	6.7