Year	Years
1970	2.13
1971	2.19
1972	2.26
1973	2.32
1974	2.39
1975	2.46
1976	2.53
1977	2.6
1978	2.67
1979	2.75
1980	2.82
1981	2.9
1982	2.98
1983	3.06
1984	3.14
1985	3.22
1986	3.31
1987	3.39
1988	3.48
1989	3.57
1990	3.66
1991	3.75
1992	3.84
1993	3.94
1994	4.03
1995	4.13
1996	4.24
1997	4.35
1998	4.46
1999	4.57
2000	4.69
2001	4.81
2002	4.93
2003	5.05
2004	5.17
2005	5.3
2006	5.43
2007	5.56
2008	5.7
2009	5.83
2010	5.97
2011	6.11
2012	6.25
2013	6.4
2014	6.54
2015	6.69