Year	Years
1970	1.72
1971	1.76
1972	1.81
1973	1.85
1974	1.9
1975	1.95
1976	2
1977	2.05
1978	2.1
1979	2.16
1980	2.21
1981	2.27
1982	2.33
1983	2.38
1984	2.44
1985	2.51
1986	2.57
1987	2.63
1988	2.7
1989	2.76
1990	2.83
1991	2.9
1992	2.97
1993	3.04
1994	3.12
1995	3.19
1996	3.27
1997	3.35
1998	3.42
1999	3.5
2000	3.59
2001	3.67
2002	3.75
2003	3.84
2004	3.93
2005	4.02
2006	4.11
2007	4.2
2008	4.29
2009	4.39
2010	4.49
2011	4.58
2012	4.68
2013	4.79
2014	4.89
2015	4.99