Year	Years
1970	2.09
1971	2.14
1972	2.19
1973	2.25
1974	2.3
1975	2.35
1976	2.41
1977	2.46
1978	2.52
1979	2.58
1980	2.64
1981	2.69
1982	2.75
1983	2.81
1984	2.87
1985	2.94
1986	3
1987	3.06
1988	3.12
1989	3.19
1990	3.25
1991	3.32
1992	3.38
1993	3.45
1994	3.51
1995	3.58
1996	3.65
1997	3.72
1998	3.8
1999	3.87
2000	3.95
2001	4.03
2002	4.12
2003	4.2
2004	4.29
2005	4.37
2006	4.46
2007	4.55
2008	4.65
2009	4.74
2010	4.84
2011	4.93
2012	5.03
2013	5.14
2014	5.24
2015	5.34