Year	Years
1970	5.06
1971	5.15
1972	5.24
1973	5.33
1974	5.43
1975	5.52
1976	5.61
1977	5.71
1978	5.81
1979	5.9
1980	6
1981	6.1
1982	6.2
1983	6.3
1984	6.4
1985	6.5
1986	6.6
1987	6.7
1988	6.8
1989	6.91
1990	7.02
1991	7.12
1992	7.23
1993	7.34
1994	7.46
1995	7.58
1996	7.71
1997	7.84
1998	7.97
1999	8.1
2000	8.24
2001	8.38
2002	8.51
2003	8.65
2004	8.79
2005	8.93
2006	9.07
2007	9.22
2008	9.36
2009	9.5
2010	9.64
2011	9.79
2012	9.93
2013	10.08
2014	10.22
2015	10.37