Year	Years
1970	1.61
1971	1.66
1972	1.7
1973	1.74
1974	1.79
1975	1.83
1976	1.88
1977	1.93
1978	1.98
1979	2.03
1980	2.08
1981	2.13
1982	2.18
1983	2.24
1984	2.29
1985	2.35
1986	2.41
1987	2.47
1988	2.53
1989	2.59
1990	2.65
1991	2.72
1992	2.78
1993	2.85
1994	2.91
1995	2.98
1996	3.05
1997	3.12
1998	3.19
1999	3.27
2000	3.34
2001	3.42
2002	3.5
2003	3.58
2004	3.66
2005	3.74
2006	3.83
2007	3.91
2008	4
2009	4.09
2010	4.18
2011	4.28
2012	4.37
2013	4.47
2014	4.57
2015	4.66