Year	Number of
1990	5.26
1991	5.28
1992	5.33
1993	5.35
1994	5.39
1995	5.42
1996	5.44
1997	5.45
1998	5.48
1999	5.51
2000	5.52
2001	5.53
2002	5.52
2003	5.54
2004	5.56
2005	5.6
2006	5.6
2007	5.63
2008	5.67
2009	5.73
2010	5.82
2011	5.89
2012	5.97
2013	6.05
2014	6.13
2015	6.21
2016	6.29