Year	Years
1970	3.02
1971	3.09
1972	3.16
1973	3.24
1974	3.31
1975	3.39
1976	3.47
1977	3.55
1978	3.64
1979	3.72
1980	3.81
1981	3.89
1982	3.98
1983	4.07
1984	4.16
1985	4.26
1986	4.35
1987	4.45
1988	4.54
1989	4.64
1990	4.74
1991	4.84
1992	4.95
1993	5.05
1994	5.16
1995	5.26
1996	5.37
1997	5.48
1998	5.59
1999	5.7
2000	5.81
2001	5.92
2002	6.04
2003	6.16
2004	6.28
2005	6.39
2006	6.52
2007	6.64
2008	6.76
2009	6.89
2010	7.01
2011	7.14
2012	7.27
2013	7.4
2014	7.53
2015	7.66