Year	Years
1970	3.24
1971	3.35
1972	3.46
1973	3.58
1974	3.69
1975	3.82
1976	3.94
1977	4.07
1978	4.21
1979	4.34
1980	4.48
1981	4.63
1982	4.78
1983	4.93
1984	5.09
1985	5.25
1986	5.42
1987	5.59
1988	5.76
1989	5.93
1990	6.11
1991	6.29
1992	6.48
1993	6.66
1994	6.85
1995	7.03
1996	7.2
1997	7.37
1998	7.53
1999	7.7
2000	7.87
2001	8.04
2002	8.2
2003	8.37
2004	8.54
2005	8.71
2006	8.87
2007	9.04
2008	9.21
2009	9.37
2010	9.54
2011	9.71
2012	9.87
2013	10.04
2014	10.2
2015	10.36