Year	Years
1970	1.83
1971	1.89
1972	1.95
1973	2.01
1974	2.07
1975	2.13
1976	2.2
1977	2.27
1978	2.34
1979	2.41
1980	2.48
1981	2.55
1982	2.63
1983	2.71
1984	2.79
1985	2.87
1986	2.96
1987	3.04
1988	3.13
1989	3.22
1990	3.32
1991	3.41
1992	3.51
1993	3.61
1994	3.71
1995	3.82
1996	3.92
1997	4.03
1998	4.14
1999	4.26
2000	4.37
2001	4.49
2002	4.61
2003	4.73
2004	4.86
2005	4.98
2006	5.11
2007	5.24
2008	5.38
2009	5.51
2010	5.65
2011	5.79
2012	5.93
2013	6.07
2014	6.22
2015	6.37