Year	Years
1970	2.06
1971	2.13
1972	2.2
1973	2.27
1974	2.35
1975	2.43
1976	2.51
1977	2.6
1978	2.69
1979	2.78
1980	2.87
1981	2.96
1982	3.06
1983	3.16
1984	3.27
1985	3.37
1986	3.48
1987	3.59
1988	3.7
1989	3.82
1990	3.94
1991	4.06
1992	4.18
1993	4.3
1994	4.43
1995	4.56
1996	4.66
1997	4.77
1998	4.88
1999	4.98
2000	5.1
2001	5.21
2002	5.32
2003	5.43
2004	5.55
2005	5.67
2006	5.79
2007	5.91
2008	6.04
2009	6.16
2010	6.29
2011	6.42
2012	6.56
2013	6.69
2014	6.83
2015	6.97