Year	Years
1970	2.43
1971	2.5
1972	2.58
1973	2.65
1974	2.73
1975	2.81
1976	2.89
1977	2.97
1978	3.06
1979	3.14
1980	3.23
1981	3.32
1982	3.42
1983	3.51
1984	3.61
1985	3.7
1986	3.8
1987	3.91
1988	4.01
1989	4.12
1990	4.22
1991	4.33
1992	4.44
1993	4.56
1994	4.67
1995	4.79
1996	4.91
1997	5.03
1998	5.15
1999	5.28
2000	5.41
2001	5.54
2002	5.67
2003	5.81
2004	5.95
2005	6.09
2006	6.23
2007	6.37
2008	6.52
2009	6.67
2010	6.82
2011	6.97
2012	7.12
2013	7.28
2014	7.44
2015	7.6