Year	Number of
1990	6.16
1991	6.26
1992	6.45
1993	6.11
1994	6.19
1995	5.89
1996	5.58
1997	5.38
1998	5.34
1999	5.3
2000	5.51
2001	5.55
2002	5.57
2003	5.5
2004	5.44
2005	5.13
2006	5.14
2007	5.05
2008	4.92
2009	4.81
2010	4.76
2011	4.69
2012	4.88
2013	4.89
2014	5.21
2015	5.32
2016	5.45