Year	Years
1970	1.98
1971	2.04
1972	2.1
1973	2.17
1974	2.23
1975	2.3
1976	2.37
1977	2.44
1978	2.51
1979	2.58
1980	2.66
1981	2.74
1982	2.82
1983	2.9
1984	2.98
1985	3.06
1986	3.15
1987	3.24
1988	3.33
1989	3.42
1990	3.52
1991	3.61
1992	3.71
1993	3.81
1994	3.92
1995	4.02
1996	4.12
1997	4.23
1998	4.34
1999	4.45
2000	4.56
2001	4.67
2002	4.79
2003	4.91
2004	5.03
2005	5.16
2006	5.28
2007	5.41
2008	5.54
2009	5.67
2010	5.81
2011	5.95
2012	6.08
2013	6.22
2014	6.37
2015	6.51