Year	Years
1970	1.61
1971	1.65
1972	1.69
1973	1.74
1974	1.78
1975	1.83
1976	1.88
1977	1.92
1978	1.97
1979	2.02
1980	2.07
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	2.66
1991	2.72
1992	2.79
1993	2.86
1994	2.93
1995	3
1996	3.07
1997	3.14
1998	3.22
1999	3.29
2000	3.37
2001	3.45
2002	3.53
2003	3.61
2004	3.7
2005	3.78
2006	3.87
2007	3.96
2008	4.05
2009	4.14
2010	4.23
2011	4.32
2012	4.42
2013	4.52
2014	4.62
2015	4.72