Year	Years
1970	2.13
1971	2.19
1972	2.26
1973	2.33
1974	2.41
1975	2.48
1976	2.56
1977	2.63
1978	2.71
1979	2.8
1980	2.88
1981	2.96
1982	3.05
1983	3.14
1984	3.23
1985	3.33
1986	3.42
1987	3.52
1988	3.61
1989	3.71
1990	3.81
1991	3.92
1992	4.02
1993	4.12
1994	4.23
1995	4.33
1996	4.43
1997	4.53
1998	4.64
1999	4.75
2000	4.86
2001	4.97
2002	5.09
2003	5.21
2004	5.33
2005	5.45
2006	5.58
2007	5.7
2008	5.83
2009	5.97
2010	6.1
2011	6.24
2012	6.38
2013	6.52
2014	6.66
2015	6.81