Year	Years
1970	2.05
1971	2.12
1972	2.18
1973	2.24
1974	2.31
1975	2.38
1976	2.45
1977	2.52
1978	2.6
1979	2.67
1980	2.75
1981	2.83
1982	2.91
1983	3
1984	3.08
1985	3.17
1986	3.26
1987	3.35
1988	3.45
1989	3.55
1990	3.65
1991	3.75
1992	3.85
1993	3.96
1994	4.07
1995	4.18
1996	4.3
1997	4.42
1998	4.55
1999	4.67
2000	4.8
2001	4.93
2002	5.06
2003	5.2
2004	5.33
2005	5.47
2006	5.62
2007	5.76
2008	5.91
2009	6.05
2010	6.2
2011	6.36
2012	6.51
2013	6.67
2014	6.82
2015	6.98