Year	Years
1970	3.24
1971	3.33
1972	3.43
1973	3.53
1974	3.63
1975	3.74
1976	3.85
1977	3.95
1978	4.07
1979	4.18
1980	4.3
1981	4.42
1982	4.54
1983	4.66
1984	4.78
1985	4.91
1986	5.04
1987	5.17
1988	5.31
1989	5.44
1990	5.58
1991	5.72
1992	5.86
1993	6
1994	6.15
1995	6.29
1996	6.44
1997	6.59
1998	6.74
1999	6.89
2000	7.04
2001	7.19
2002	7.35
2003	7.5
2004	7.66
2005	7.81
2006	7.97
2007	8.13
2008	8.29
2009	8.45
2010	8.61
2011	8.77
2012	8.93
2013	9.09
2014	9.26
2015	9.42