Year	Years
1970	2.18
1971	2.24
1972	2.29
1973	2.35
1974	2.41
1975	2.47
1976	2.53
1977	2.59
1978	2.66
1979	2.72
1980	2.79
1981	2.86
1982	2.92
1983	2.99
1984	3.06
1985	3.14
1986	3.21
1987	3.28
1988	3.36
1989	3.43
1990	3.51
1991	3.59
1992	3.67
1993	3.74
1994	3.83
1995	3.91
1996	3.99
1997	4.07
1998	4.16
1999	4.25
2000	4.33
2001	4.42
2002	4.52
2003	4.61
2004	4.7
2005	4.8
2006	4.9
2007	5
2008	5.1
2009	5.2
2010	5.31
2011	5.41
2012	5.52
2013	5.63
2014	5.74
2015	5.85