Year	Years
1970	2.49
1971	2.57
1972	2.65
1973	2.73
1974	2.82
1975	2.91
1976	2.99
1977	3.09
1978	3.18
1979	3.27
1980	3.37
1981	3.47
1982	3.58
1983	3.68
1984	3.79
1985	3.9
1986	4.01
1987	4.13
1988	4.25
1989	4.36
1990	4.49
1991	4.61
1992	4.74
1993	4.86
1994	4.99
1995	5.13
1996	5.26
1997	5.4
1998	5.54
1999	5.69
2000	5.83
2001	5.97
2002	6.12
2003	6.26
2004	6.41
2005	6.56
2006	6.71
2007	6.86
2008	7.01
2009	7.16
2010	7.31
2011	7.46
2012	7.62
2013	7.77
2014	7.92
2015	8.08