Year	Years
1970	3.17
1971	3.24
1972	3.32
1973	3.4
1974	3.48
1975	3.56
1976	3.64
1977	3.72
1978	3.81
1979	3.89
1980	3.98
1981	4.07
1982	4.16
1983	4.25
1984	4.34
1985	4.44
1986	4.53
1987	4.63
1988	4.73
1989	4.83
1990	4.93
1991	5.03
1992	5.13
1993	5.24
1994	5.34
1995	5.45
1996	5.56
1997	5.67
1998	5.78
1999	5.89
2000	6.01
2001	6.13
2002	6.24
2003	6.36
2004	6.48
2005	6.61
2006	6.73
2007	6.85
2008	6.98
2009	7.11
2010	7.24
2011	7.37
2012	7.5
2013	7.63
2014	7.76
2015	7.9