Year	Years
1970	3.63
1971	3.73
1972	3.84
1973	3.94
1974	4.05
1975	4.16
1976	4.27
1977	4.38
1978	4.5
1979	4.61
1980	4.73
1981	4.85
1982	4.98
1983	5.1
1984	5.23
1985	5.36
1986	5.49
1987	5.62
1988	5.76
1989	5.89
1990	6.03
1991	6.17
1992	6.31
1993	6.46
1994	6.6
1995	6.75
1996	6.9
1997	7.05
1998	7.2
1999	7.35
2000	7.5
2001	7.66
2002	7.82
2003	7.98
2004	8.14
2005	8.3
2006	8.46
2007	8.63
2008	8.79
2009	8.96
2010	9.13
2011	9.29
2012	9.46
2013	9.63
2014	9.8
2015	9.97