Year	Years
1970	4.11
1971	4.2
1972	4.3
1973	4.39
1974	4.49
1975	4.58
1976	4.68
1977	4.78
1978	4.88
1979	4.98
1980	5.09
1981	5.19
1982	5.3
1983	5.4
1984	5.51
1985	5.62
1986	5.73
1987	5.84
1988	5.95
1989	6.06
1990	6.17
1991	6.28
1992	6.39
1993	6.51
1994	6.62
1995	6.73
1996	6.83
1997	6.94
1998	7.05
1999	7.16
2000	7.27
2001	7.39
2002	7.5
2003	7.62
2004	7.74
2005	7.86
2006	7.98
2007	8.1
2008	8.23
2009	8.35
2010	8.48
2011	8.6
2012	8.73
2013	8.86
2014	8.99
2015	9.12