Year	Years
1970	1.88
1971	1.92
1972	1.97
1973	2.02
1974	2.07
1975	2.12
1976	2.18
1977	2.23
1978	2.29
1979	2.34
1980	2.4
1981	2.46
1982	2.52
1983	2.58
1984	2.64
1985	2.71
1986	2.77
1987	2.84
1988	2.9
1989	2.97
1990	3.04
1991	3.11
1992	3.19
1993	3.26
1994	3.33
1995	3.41
1996	3.49
1997	3.56
1998	3.64
1999	3.73
2000	3.81
2001	3.89
2002	3.98
2003	4.07
2004	4.16
2005	4.25
2006	4.34
2007	4.44
2008	4.53
2009	4.63
2010	4.73
2011	4.83
2012	4.94
2013	5.04
2014	5.15
2015	5.26