Year	Years
1970	1.87
1971	1.91
1972	1.96
1973	2.01
1974	2.06
1975	2.11
1976	2.16
1977	2.22
1978	2.27
1979	2.32
1980	2.38
1981	2.44
1982	2.5
1983	2.56
1984	2.62
1985	2.68
1986	2.74
1987	2.81
1988	2.87
1989	2.94
1990	3
1991	3.07
1992	3.14
1993	3.21
1994	3.29
1995	3.36
1996	3.44
1997	3.51
1998	3.59
1999	3.67
2000	3.76
2001	3.84
2002	3.93
2003	4.01
2004	4.1
2005	4.19
2006	4.29
2007	4.38
2008	4.48
2009	4.57
2010	4.67
2011	4.77
2012	4.87
2013	4.98
2014	5.08
2015	5.19