Year	Years
1970	3.19
1971	3.28
1972	3.36
1973	3.45
1974	3.54
1975	3.63
1976	3.73
1977	3.83
1978	3.93
1979	4.03
1980	4.13
1981	4.24
1982	4.34
1983	4.45
1984	4.57
1985	4.68
1986	4.8
1987	4.91
1988	5.04
1989	5.16
1990	5.28
1991	5.41
1992	5.54
1993	5.66
1994	5.79
1995	5.93
1996	6.05
1997	6.18
1998	6.3
1999	6.43
2000	6.56
2001	6.69
2002	6.82
2003	6.95
2004	7.08
2005	7.21
2006	7.34
2007	7.47
2008	7.6
2009	7.73
2010	7.87
2011	8
2012	8.13
2013	8.26
2014	8.4
2015	8.53