Year	Years
1970	1.67
1971	1.71
1972	1.76
1973	1.8
1974	1.85
1975	1.9
1976	1.95
1977	2
1978	2.05
1979	2.1
1980	2.16
1981	2.21
1982	2.27
1983	2.33
1984	2.39
1985	2.45
1986	2.51
1987	2.57
1988	2.64
1989	2.7
1990	2.77
1991	2.84
1992	2.91
1993	2.99
1994	3.06
1995	3.14
1996	3.22
1997	3.3
1998	3.38
1999	3.47
2000	3.56
2001	3.64
2002	3.73
2003	3.82
2004	3.92
2005	4.01
2006	4.11
2007	4.2
2008	4.3
2009	4.4
2010	4.5
2011	4.61
2012	4.71
2013	4.81
2014	4.92
2015	5.03