Year	Years
1970	3.45
1971	3.53
1972	3.61
1973	3.69
1974	3.77
1975	3.85
1976	3.94
1977	4.03
1978	4.12
1979	4.21
1980	4.3
1981	4.39
1982	4.48
1983	4.58
1984	4.67
1985	4.77
1986	4.87
1987	4.97
1988	5.07
1989	5.18
1990	5.28
1991	5.39
1992	5.49
1993	5.6
1994	5.71
1995	5.82
1996	5.93
1997	6.05
1998	6.17
1999	6.28
2000	6.4
2001	6.53
2002	6.65
2003	6.77
2004	6.9
2005	7.03
2006	7.16
2007	7.29
2008	7.42
2009	7.55
2010	7.68
2011	7.82
2012	7.95
2013	8.09
2014	8.22
2015	8.36