Year	Years
1970	3.65
1971	3.74
1972	3.84
1973	3.93
1974	4.03
1975	4.13
1976	4.23
1977	4.33
1978	4.44
1979	4.54
1980	4.65
1981	4.76
1982	4.87
1983	4.99
1984	5.1
1985	5.22
1986	5.34
1987	5.46
1988	5.58
1989	5.7
1990	5.82
1991	5.95
1992	6.07
1993	6.2
1994	6.32
1995	6.45
1996	6.57
1997	6.69
1998	6.82
1999	6.94
2000	7.06
2001	7.18
2002	7.31
2003	7.43
2004	7.55
2005	7.68
2006	7.8
2007	7.92
2008	8.05
2009	8.17
2010	8.3
2011	8.42
2012	8.55
2013	8.68
2014	8.81
2015	8.93