Year	Years
1970	1.7
1971	1.74
1972	1.79
1973	1.84
1974	1.9
1975	1.95
1976	2.01
1977	2.07
1978	2.13
1979	2.19
1980	2.25
1981	2.32
1982	2.38
1983	2.45
1984	2.53
1985	2.6
1986	2.68
1987	2.76
1988	2.84
1989	2.92
1990	3.01
1991	3.1
1992	3.19
1993	3.29
1994	3.38
1995	3.49
1996	3.58
1997	3.67
1998	3.77
1999	3.87
2000	3.96
2001	4.06
2002	4.16
2003	4.26
2004	4.36
2005	4.46
2006	4.57
2007	4.67
2008	4.78
2009	4.88
2010	4.99
2011	5.1
2012	5.21
2013	5.32
2014	5.43
2015	5.54