Year	Years
1970	1.56
1971	1.6
1972	1.64
1973	1.69
1974	1.73
1975	1.78
1976	1.83
1977	1.88
1978	1.93
1979	1.98
1980	2.03
1981	2.09
1982	2.14
1983	2.2
1984	2.26
1985	2.32
1986	2.38
1987	2.45
1988	2.51
1989	2.58
1990	2.65
1991	2.73
1992	2.8
1993	2.88
1994	2.96
1995	3.04
1996	3.12
1997	3.21
1998	3.29
1999	3.38
2000	3.47
2001	3.56
2002	3.65
2003	3.75
2004	3.84
2005	3.94
2006	4.03
2007	4.13
2008	4.23
2009	4.33
2010	4.43
2011	4.53
2012	4.64
2013	4.74
2014	4.85
2015	4.96