Year	Years
1970	1.61
1971	1.65
1972	1.7
1973	1.75
1974	1.8
1975	1.84
1976	1.9
1977	1.95
1978	2
1979	2.06
1980	2.11
1981	2.17
1982	2.23
1983	2.3
1984	2.36
1985	2.43
1986	2.49
1987	2.56
1988	2.64
1989	2.71
1990	2.79
1991	2.87
1992	2.95
1993	3.03
1994	3.12
1995	3.21
1996	3.31
1997	3.41
1998	3.51
1999	3.61
2000	3.72
2001	3.82
2002	3.93
2003	4.03
2004	4.14
2005	4.25
2006	4.35
2007	4.46
2008	4.57
2009	4.69
2010	4.8
2011	4.91
2012	5.03
2013	5.14
2014	5.26
2015	5.38