Year	Years
1970	1.42
1971	1.46
1972	1.51
1973	1.56
1974	1.61
1975	1.66
1976	1.71
1977	1.76
1978	1.82
1979	1.88
1980	1.94
1981	2
1982	2.06
1983	2.12
1984	2.19
1985	2.26
1986	2.33
1987	2.4
1988	2.47
1989	2.55
1990	2.63
1991	2.71
1992	2.79
1993	2.87
1994	2.96
1995	3.05
1996	3.14
1997	3.24
1998	3.33
1999	3.43
2000	3.53
2001	3.64
2002	3.74
2003	3.85
2004	3.96
2005	4.07
2006	4.19
2007	4.3
2008	4.42
2009	4.54
2010	4.66
2011	4.79
2012	4.92
2013	5.04
2014	5.18
2015	5.31