Year	Years
1970	3.26
1971	3.37
1972	3.48
1973	3.6
1974	3.72
1975	3.84
1976	3.96
1977	4.09
1978	4.21
1979	4.34
1980	4.47
1981	4.61
1982	4.74
1983	4.88
1984	5.02
1985	5.16
1986	5.3
1987	5.44
1988	5.58
1989	5.73
1990	5.87
1991	6.02
1992	6.16
1993	6.31
1994	6.45
1995	6.59
1996	6.71
1997	6.83
1998	6.95
1999	7.07
2000	7.19
2001	7.32
2002	7.44
2003	7.57
2004	7.7
2005	7.83
2006	7.96
2007	8.09
2008	8.23
2009	8.37
2010	8.51
2011	8.66
2012	8.8
2013	8.95
2014	9.1
2015	9.26