Year	Years
1970	1.94
1971	2
1972	2.06
1973	2.13
1974	2.19
1975	2.26
1976	2.33
1977	2.41
1978	2.48
1979	2.56
1980	2.63
1981	2.71
1982	2.8
1983	2.88
1984	2.97
1985	3.06
1986	3.15
1987	3.24
1988	3.34
1989	3.44
1990	3.54
1991	3.65
1992	3.75
1993	3.86
1994	3.97
1995	4.09
1996	4.21
1997	4.34
1998	4.47
1999	4.6
2000	4.73
2001	4.87
2002	5
2003	5.14
2004	5.28
2005	5.42
2006	5.57
2007	5.71
2008	5.86
2009	6.01
2010	6.15
2011	6.31
2012	6.46
2013	6.61
2014	6.77
2015	6.92