Year	Number of
1990	6.18
1991	6.36
1992	6.44
1993	6.23
1994	6.4
1995	6.19
1996	5.96
1997	5.68
1998	5.63
1999	5.49
2000	5.3
2001	5.13
2002	5.2
2003	5.11
2004	4.89
2005	4.68
2006	4.65
2007	4.41
2008	4.46
2009	4.53
2010	4.55
2011	4.66
2012	4.72
2013	4.89
2014	5.01
2015	4.99
2016	5.07