Year	Years
1970	1.34
1971	1.38
1972	1.43
1973	1.47
1974	1.52
1975	1.57
1976	1.62
1977	1.67
1978	1.72
1979	1.77
1980	1.83
1981	1.88
1982	1.94
1983	2
1984	2.06
1985	2.12
1986	2.18
1987	2.25
1988	2.31
1989	2.38
1990	2.45
1991	2.52
1992	2.59
1993	2.66
1994	2.74
1995	2.81
1996	2.89
1997	2.97
1998	3.05
1999	3.13
2000	3.22
2001	3.3
2002	3.39
2003	3.48
2004	3.57
2005	3.67
2006	3.77
2007	3.86
2008	3.97
2009	4.07
2010	4.18
2011	4.29
2012	4.4
2013	4.51
2014	4.63
2015	4.75