Year	Years
1970	1.69
1971	1.73
1972	1.78
1973	1.82
1974	1.87
1975	1.92
1976	1.96
1977	2.01
1978	2.07
1979	2.12
1980	2.17
1981	2.22
1982	2.28
1983	2.34
1984	2.39
1985	2.45
1986	2.51
1987	2.58
1988	2.64
1989	2.7
1990	2.77
1991	2.83
1992	2.9
1993	2.97
1994	3.04
1995	3.12
1996	3.19
1997	3.27
1998	3.34
1999	3.42
2000	3.5
2001	3.59
2002	3.67
2003	3.76
2004	3.84
2005	3.93
2006	4.02
2007	4.11
2008	4.21
2009	4.3
2010	4.4
2011	4.49
2012	4.59
2013	4.69
2014	4.8
2015	4.9