Year	Years
1970	1.73
1971	1.78
1972	1.82
1973	1.87
1974	1.92
1975	1.97
1976	2.02
1977	2.07
1978	2.13
1979	2.18
1980	2.24
1981	2.3
1982	2.36
1983	2.42
1984	2.48
1985	2.54
1986	2.61
1987	2.68
1988	2.75
1989	2.82
1990	2.89
1991	2.97
1992	3.04
1993	3.12
1994	3.21
1995	3.29
1996	3.38
1997	3.47
1998	3.57
1999	3.66
2000	3.76
2001	3.85
2002	3.95
2003	4.05
2004	4.15
2005	4.26
2006	4.36
2007	4.47
2008	4.57
2009	4.68
2010	4.79
2011	4.9
2012	5.01
2013	5.12
2014	5.24
2015	5.35