Year	Years
1970	1.46
1971	1.51
1972	1.56
1973	1.62
1974	1.68
1975	1.74
1976	1.8
1977	1.87
1978	1.94
1979	2.01
1980	2.09
1981	2.17
1982	2.25
1983	2.34
1984	2.44
1985	2.54
1986	2.64
1987	2.76
1988	2.88
1989	3.01
1990	3.14
1991	3.29
1992	3.45
1993	3.61
1994	3.79
1995	3.98
1996	4.13
1997	4.28
1998	4.43
1999	4.58
2000	4.73
2001	4.88
2002	5.02
2003	5.17
2004	5.31
2005	5.45
2006	5.6
2007	5.74
2008	5.88
2009	6.02
2010	6.16
2011	6.3
2012	6.43
2013	6.57
2014	6.7
2015	6.84