Year	Years
1970	1.88
1971	1.95
1972	2.01
1973	2.09
1974	2.16
1975	2.23
1976	2.31
1977	2.39
1978	2.48
1979	2.56
1980	2.65
1981	2.75
1982	2.84
1983	2.94
1984	3.04
1985	3.15
1986	3.26
1987	3.37
1988	3.49
1989	3.61
1990	3.73
1991	3.86
1992	3.99
1993	4.12
1994	4.26
1995	4.4
1996	4.53
1997	4.67
1998	4.8
1999	4.94
2000	5.08
2001	5.22
2002	5.37
2003	5.51
2004	5.65
2005	5.8
2006	5.95
2007	6.1
2008	6.24
2009	6.39
2010	6.54
2011	6.69
2012	6.85
2013	7
2014	7.15
2015	7.3