Year	Years
1970	3.11
1971	3.18
1972	3.25
1973	3.33
1974	3.4
1975	3.48
1976	3.56
1977	3.64
1978	3.73
1979	3.81
1980	3.89
1981	3.98
1982	4.07
1983	4.16
1984	4.25
1985	4.35
1986	4.44
1987	4.54
1988	4.63
1989	4.73
1990	4.83
1991	4.94
1992	5.04
1993	5.14
1994	5.25
1995	5.36
1996	5.47
1997	5.59
1998	5.7
1999	5.82
2000	5.94
2001	6.06
2002	6.18
2003	6.3
2004	6.42
2005	6.55
2006	6.67
2007	6.8
2008	6.93
2009	7.05
2010	7.18
2011	7.31
2012	7.44
2013	7.58
2014	7.71
2015	7.84