Year	Years
1970	1.89
1971	1.95
1972	2.01
1973	2.08
1974	2.15
1975	2.22
1976	2.29
1977	2.37
1978	2.45
1979	2.53
1980	2.61
1981	2.69
1982	2.78
1983	2.87
1984	2.96
1985	3.05
1986	3.14
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	4.08
1996	4.19
1997	4.3
1998	4.42
1999	4.53
2000	4.65
2001	4.76
2002	4.88
2003	5
2004	5.11
2005	5.23
2006	5.35
2007	5.47
2008	5.59
2009	5.72
2010	5.84
2011	5.96
2012	6.09
2013	6.22
2014	6.34
2015	6.47