Year	Years
1970	2.59
1971	2.66
1972	2.73
1973	2.8
1974	2.87
1975	2.94
1976	3.02
1977	3.09
1978	3.17
1979	3.26
1980	3.34
1981	3.42
1982	3.51
1983	3.6
1984	3.69
1985	3.79
1986	3.89
1987	3.99
1988	4.09
1989	4.19
1990	4.3
1991	4.41
1992	4.53
1993	4.65
1994	4.77
1995	4.89
1996	5.02
1997	5.15
1998	5.28
1999	5.41
2000	5.54
2001	5.68
2002	5.81
2003	5.94
2004	6.08
2005	6.21
2006	6.35
2007	6.49
2008	6.62
2009	6.76
2010	6.89
2011	7.03
2012	7.17
2013	7.3
2014	7.44
2015	7.58