Year	Years
1970	1.42
1971	1.46
1972	1.5
1973	1.55
1974	1.59
1975	1.63
1976	1.68
1977	1.72
1978	1.77
1979	1.82
1980	1.87
1981	1.92
1982	1.97
1983	2.03
1984	2.08
1985	2.14
1986	2.2
1987	2.26
1988	2.32
1989	2.38
1990	2.45
1991	2.51
1992	2.58
1993	2.65
1994	2.72
1995	2.79
1996	2.86
1997	2.94
1998	3.02
1999	3.09
2000	3.17
2001	3.25
2002	3.33
2003	3.41
2004	3.5
2005	3.58
2006	3.67
2007	3.75
2008	3.84
2009	3.93
2010	4.02
2011	4.11
2012	4.2
2013	4.29
2014	4.38
2015	4.48