Year	Years
1970	1.74
1971	1.79
1972	1.83
1973	1.88
1974	1.93
1975	1.98
1976	2.03
1977	2.08
1978	2.13
1979	2.18
1980	2.24
1981	2.29
1982	2.35
1983	2.41
1984	2.47
1985	2.53
1986	2.59
1987	2.65
1988	2.72
1989	2.78
1990	2.85
1991	2.92
1992	2.99
1993	3.06
1994	3.13
1995	3.2
1996	3.27
1997	3.34
1998	3.42
1999	3.49
2000	3.57
2001	3.65
2002	3.73
2003	3.81
2004	3.89
2005	3.97
2006	4.06
2007	4.15
2008	4.24
2009	4.33
2010	4.42
2011	4.51
2012	4.61
2013	4.71
2014	4.8
2015	4.9