Year	Number of
1990	6.56
1991	6.43
1992	6.44
1993	6.52
1994	6.39
1995	6.05
1996	6.38
1997	6.05
1998	6.21
1999	6.05
2000	6.09
2001	5.5
2002	5.42
2003	5.33
2004	5.17
2005	5.05
2006	5.21
2007	5.14
2008	5.17
2009	5.13
2010	5.2
2011	5.21
2012	5.36
2013	5.46
2014	5.65
2015	5.64
2016	6.15