Year	Years
1970	1.87
1971	1.92
1972	1.98
1973	2.04
1974	2.1
1975	2.16
1976	2.22
1977	2.29
1978	2.35
1979	2.42
1980	2.49
1981	2.55
1982	2.63
1983	2.7
1984	2.77
1985	2.84
1986	2.92
1987	2.99
1988	3.07
1989	3.15
1990	3.23
1991	3.3
1992	3.38
1993	3.46
1994	3.54
1995	3.62
1996	3.69
1997	3.77
1998	3.85
1999	3.93
2000	4.01
2001	4.1
2002	4.19
2003	4.28
2004	4.38
2005	4.48
2006	4.58
2007	4.68
2008	4.79
2009	4.9
2010	5.01
2011	5.13
2012	5.25
2013	5.37
2014	5.49
2015	5.61