Year	Years
1970	1.54
1971	1.58
1972	1.62
1973	1.66
1974	1.7
1975	1.75
1976	1.79
1977	1.84
1978	1.89
1979	1.93
1980	1.98
1981	2.03
1982	2.08
1983	2.14
1984	2.19
1985	2.24
1986	2.3
1987	2.35
1988	2.41
1989	2.47
1990	2.53
1991	2.59
1992	2.65
1993	2.71
1994	2.77
1995	2.83
1996	2.9
1997	2.96
1998	3.03
1999	3.1
2000	3.17
2001	3.24
2002	3.32
2003	3.39
2004	3.47
2005	3.55
2006	3.63
2007	3.71
2008	3.8
2009	3.88
2010	3.97
2011	4.06
2012	4.15
2013	4.25
2014	4.34
2015	4.44