Year	Years
1970	1.95
1971	2
1972	2.05
1973	2.1
1974	2.15
1975	2.2
1976	2.26
1977	2.32
1978	2.37
1979	2.43
1980	2.49
1981	2.55
1982	2.61
1983	2.68
1984	2.74
1985	2.81
1986	2.88
1987	2.94
1988	3.01
1989	3.08
1990	3.16
1991	3.23
1992	3.3
1993	3.38
1994	3.46
1995	3.54
1996	3.62
1997	3.71
1998	3.79
1999	3.88
2000	3.97
2001	4.06
2002	4.16
2003	4.25
2004	4.34
2005	4.44
2006	4.54
2007	4.64
2008	4.74
2009	4.84
2010	4.94
2011	5.04
2012	5.15
2013	5.26
2014	5.37
2015	5.48