Year	Years
1970	2.46
1971	2.52
1972	2.59
1973	2.65
1974	2.71
1975	2.78
1976	2.85
1977	2.92
1978	2.99
1979	3.06
1980	3.13
1981	3.2
1982	3.28
1983	3.36
1984	3.43
1985	3.51
1986	3.6
1987	3.68
1988	3.76
1989	3.85
1990	3.93
1991	4.02
1992	4.11
1993	4.2
1994	4.29
1995	4.39
1996	4.48
1997	4.57
1998	4.67
1999	4.77
2000	4.87
2001	4.97
2002	5.07
2003	5.18
2004	5.28
2005	5.39
2006	5.5
2007	5.61
2008	5.73
2009	5.84
2010	5.96
2011	6.07
2012	6.19
2013	6.31
2014	6.43
2015	6.56