Year	Years
1970	2.61
1971	2.7
1972	2.78
1973	2.87
1974	2.96
1975	3.06
1976	3.16
1977	3.26
1978	3.36
1979	3.46
1980	3.57
1981	3.68
1982	3.8
1983	3.92
1984	4.04
1985	4.17
1986	4.29
1987	4.43
1988	4.56
1989	4.7
1990	4.84
1991	4.99
1992	5.14
1993	5.29
1994	5.45
1995	5.61
1996	5.77
1997	5.93
1998	6.09
1999	6.26
2000	6.42
2001	6.58
2002	6.74
2003	6.9
2004	7.06
2005	7.23
2006	7.39
2007	7.55
2008	7.71
2009	7.87
2010	8.04
2011	8.2
2012	8.36
2013	8.52
2014	8.69
2015	8.85