Year	Years
1970	4.29
1971	4.38
1972	4.48
1973	4.58
1974	4.68
1975	4.78
1976	4.89
1977	4.99
1978	5.1
1979	5.21
1980	5.32
1981	5.43
1982	5.54
1983	5.65
1984	5.77
1985	5.89
1986	6.01
1987	6.13
1988	6.25
1989	6.37
1990	6.5
1991	6.62
1992	6.75
1993	6.88
1994	7.01
1995	7.14
1996	7.27
1997	7.41
1998	7.55
1999	7.68
2000	7.82
2001	7.96
2002	8.1
2003	8.23
2004	8.37
2005	8.51
2006	8.65
2007	8.79
2008	8.94
2009	9.08
2010	9.22
2011	9.36
2012	9.5
2013	9.64
2014	9.78
2015	9.93