Year	Years
1970	3.15
1971	3.24
1972	3.33
1973	3.43
1974	3.53
1975	3.63
1976	3.74
1977	3.84
1978	3.95
1979	4.07
1980	4.18
1981	4.3
1982	4.42
1983	4.54
1984	4.67
1985	4.8
1986	4.93
1987	5.06
1988	5.19
1989	5.33
1990	5.47
1991	5.6
1992	5.74
1993	5.88
1994	6.01
1995	6.15
1996	6.28
1997	6.41
1998	6.54
1999	6.67
2000	6.8
2001	6.93
2002	7.07
2003	7.2
2004	7.33
2005	7.46
2006	7.6
2007	7.73
2008	7.86
2009	7.99
2010	8.13
2011	8.26
2012	8.4
2013	8.53
2014	8.66
2015	8.8