Year	Number of
1990	5
1991	4.99
1992	5
1993	5.04
1994	4.96
1995	5.06
1996	5.21
1997	5.32
1998	5.53
1999	5.54
2000	5.55
2001	5.57
2002	5.59
2003	5.59
2004	5.59
2005	5.57
2006	5.55
2007	5.37
2008	5.34
2009	5.37
2010	5.27
2011	5.29
2012	5.56
2013	5.47
2014	5.46
2015	5.48
2016	5.56