Year	Years
1970	0.91
1971	0.95
1972	0.98
1973	1.02
1974	1.06
1975	1.11
1976	1.15
1977	1.2
1978	1.25
1979	1.3
1980	1.35
1981	1.41
1982	1.46
1983	1.52
1984	1.59
1985	1.65
1986	1.72
1987	1.79
1988	1.86
1989	1.94
1990	2.02
1991	2.1
1992	2.19
1993	2.27
1994	2.36
1995	2.45
1996	2.54
1997	2.62
1998	2.71
1999	2.8
2000	2.89
2001	2.98
2002	3.07
2003	3.16
2004	3.26
2005	3.35
2006	3.45
2007	3.55
2008	3.65
2009	3.75
2010	3.85
2011	3.95
2012	4.06
2013	4.16
2014	4.27
2015	4.38