Year	Years
1970	1.62
1971	1.66
1972	1.7
1973	1.75
1974	1.79
1975	1.84
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	2.92
1995	2.99
1996	3.06
1997	3.13
1998	3.21
1999	3.28
2000	3.36
2001	3.44
2002	3.52
2003	3.6
2004	3.69
2005	3.77
2006	3.86
2007	3.95
2008	4.04
2009	4.14
2010	4.23
2011	4.33
2012	4.42
2013	4.52
2014	4.62
2015	4.73