Year	Years
1970	1.57
1971	1.62
1972	1.67
1973	1.72
1974	1.78
1975	1.84
1976	1.9
1977	1.96
1978	2.03
1979	2.1
1980	2.17
1981	2.24
1982	2.32
1983	2.4
1984	2.48
1985	2.57
1986	2.66
1987	2.76
1988	2.86
1989	2.97
1990	3.08
1991	3.2
1992	3.33
1993	3.47
1994	3.62
1995	3.77
1996	3.89
1997	4
1998	4.12
1999	4.23
2000	4.35
2001	4.47
2002	4.58
2003	4.7
2004	4.82
2005	4.93
2006	5.05
2007	5.17
2008	5.29
2009	5.41
2010	5.54
2011	5.66
2012	5.78
2013	5.91
2014	6.03
2015	6.16