Year	Years
1970	2
1971	2.04
1972	2.08
1973	2.13
1974	2.17
1975	2.21
1976	2.25
1977	2.3
1978	2.34
1979	2.39
1980	2.43
1981	2.48
1982	2.53
1983	2.58
1984	2.63
1985	2.68
1986	2.73
1987	2.79
1988	2.84
1989	2.9
1990	2.96
1991	3.02
1992	3.08
1993	3.15
1994	3.22
1995	3.29
1996	3.38
1997	3.46
1998	3.55
1999	3.64
2000	3.73
2001	3.83
2002	3.92
2003	4.02
2004	4.11
2005	4.21
2006	4.31
2007	4.41
2008	4.52
2009	4.62
2010	4.72
2011	4.83
2012	4.93
2013	5.04
2014	5.15
2015	5.26