Year	Years
1970	2.19
1971	2.26
1972	2.34
1973	2.42
1974	2.5
1975	2.59
1976	2.68
1977	2.77
1978	2.86
1979	2.96
1980	3.07
1981	3.17
1982	3.29
1983	3.4
1984	3.53
1985	3.65
1986	3.79
1987	3.92
1988	4.07
1989	4.22
1990	4.39
1991	4.56
1992	4.74
1993	4.93
1994	5.13
1995	5.35
1996	5.57
1997	5.79
1998	6.01
1999	6.23
2000	6.44
2001	6.65
2002	6.86
2003	7.07
2004	7.28
2005	7.48
2006	7.69
2007	7.89
2008	8.09
2009	8.29
2010	8.49
2011	8.69
2012	8.88
2013	9.08
2014	9.27
2015	9.47