Year	Years
1970	3.32
1971	3.4
1972	3.48
1973	3.56
1974	3.64
1975	3.73
1976	3.82
1977	3.9
1978	3.99
1979	4.08
1980	4.18
1981	4.27
1982	4.37
1983	4.46
1984	4.56
1985	4.66
1986	4.76
1987	4.87
1988	4.97
1989	5.07
1990	5.18
1991	5.29
1992	5.39
1993	5.5
1994	5.61
1995	5.72
1996	5.83
1997	5.95
1998	6.06
1999	6.18
2000	6.29
2001	6.41
2002	6.53
2003	6.65
2004	6.77
2005	6.89
2006	7.01
2007	7.14
2008	7.26
2009	7.39
2010	7.52
2011	7.65
2012	7.78
2013	7.91
2014	8.04
2015	8.17