Year	Years
1970	4.75
1971	4.85
1972	4.95
1973	5.05
1974	5.15
1975	5.26
1976	5.36
1977	5.47
1978	5.58
1979	5.69
1980	5.8
1981	5.91
1982	6.02
1983	6.13
1984	6.25
1985	6.36
1986	6.48
1987	6.59
1988	6.71
1989	6.83
1990	6.95
1991	7.07
1992	7.19
1993	7.31
1994	7.44
1995	7.56
1996	7.69
1997	7.82
1998	7.96
1999	8.09
2000	8.23
2001	8.36
2002	8.5
2003	8.64
2004	8.78
2005	8.92
2006	9.06
2007	9.2
2008	9.34
2009	9.48
2010	9.62
2011	9.76
2012	9.9
2013	10.05
2014	10.19
2015	10.33