Year	Years
1970	1.48
1971	1.52
1972	1.57
1973	1.61
1974	1.65
1975	1.7
1976	1.75
1977	1.8
1978	1.85
1979	1.9
1980	1.95
1981	2
1982	2.06
1983	2.12
1984	2.18
1985	2.23
1986	2.3
1987	2.36
1988	2.42
1989	2.49
1990	2.55
1991	2.62
1992	2.69
1993	2.76
1994	2.83
1995	2.9
1996	2.97
1997	3.04
1998	3.11
1999	3.18
2000	3.25
2001	3.32
2002	3.4
2003	3.47
2004	3.55
2005	3.63
2006	3.71
2007	3.79
2008	3.87
2009	3.95
2010	4.04
2011	4.12
2012	4.21
2013	4.3
2014	4.38
2015	4.47