Year	Years
1970	3.9
1971	3.98
1972	4.07
1973	4.17
1974	4.26
1975	4.35
1976	4.45
1977	4.54
1978	4.64
1979	4.74
1980	4.84
1981	4.95
1982	5.05
1983	5.15
1984	5.26
1985	5.36
1986	5.47
1987	5.58
1988	5.69
1989	5.8
1990	5.91
1991	6.02
1992	6.13
1993	6.24
1994	6.35
1995	6.47
1996	6.58
1997	6.7
1998	6.82
1999	6.93
2000	7.05
2001	7.18
2002	7.3
2003	7.42
2004	7.55
2005	7.68
2006	7.81
2007	7.94
2008	8.07
2009	8.2
2010	8.33
2011	8.47
2012	8.6
2013	8.74
2014	8.88
2015	9.01