Year	Years
1970	2.09
1971	2.16
1972	2.23
1973	2.31
1974	2.39
1975	2.47
1976	2.55
1977	2.64
1978	2.73
1979	2.82
1980	2.92
1981	3.02
1982	3.12
1983	3.23
1984	3.34
1985	3.45
1986	3.57
1987	3.69
1988	3.82
1989	3.95
1990	4.09
1991	4.23
1992	4.38
1993	4.53
1994	4.69
1995	4.86
1996	5.02
1997	5.18
1998	5.35
1999	5.52
2000	5.69
2001	5.86
2002	6.03
2003	6.21
2004	6.38
2005	6.56
2006	6.74
2007	6.92
2008	7.1
2009	7.28
2010	7.46
2011	7.63
2012	7.81
2013	7.99
2014	8.17
2015	8.34