Year	Years
1970	4.11
1971	4.21
1972	4.32
1973	4.43
1974	4.55
1975	4.66
1976	4.78
1977	4.89
1978	5.01
1979	5.13
1980	5.25
1981	5.37
1982	5.5
1983	5.62
1984	5.75
1985	5.87
1986	6
1987	6.12
1988	6.25
1989	6.38
1990	6.5
1991	6.63
1992	6.76
1993	6.88
1994	7.01
1995	7.13
1996	7.25
1997	7.38
1998	7.51
1999	7.64
2000	7.77
2001	7.91
2002	8.05
2003	8.19
2004	8.33
2005	8.48
2006	8.63
2007	8.77
2008	8.92
2009	9.08
2010	9.23
2011	9.38
2012	9.54
2013	9.7
2014	9.85
2015	10.01