Year	Years
1970	1.64
1971	1.68
1972	1.73
1973	1.77
1974	1.82
1975	1.87
1976	1.91
1977	1.97
1978	2.02
1979	2.07
1980	2.12
1981	2.18
1982	2.23
1983	2.29
1984	2.35
1985	2.41
1986	2.47
1987	2.54
1988	2.6
1989	2.67
1990	2.74
1991	2.81
1992	2.88
1993	2.95
1994	3.02
1995	3.1
1996	3.18
1997	3.25
1998	3.33
1999	3.41
2000	3.5
2001	3.58
2002	3.66
2003	3.75
2004	3.84
2005	3.93
2006	4.02
2007	4.11
2008	4.2
2009	4.3
2010	4.4
2011	4.49
2012	4.59
2013	4.7
2014	4.8
2015	4.9