Year	Years
1970	4.75
1971	4.86
1972	4.96
1973	5.07
1974	5.18
1975	5.29
1976	5.4
1977	5.51
1978	5.62
1979	5.73
1980	5.85
1981	5.96
1982	6.08
1983	6.19
1984	6.31
1985	6.43
1986	6.55
1987	6.66
1988	6.78
1989	6.9
1990	7.02
1991	7.14
1992	7.26
1993	7.38
1994	7.5
1995	7.62
1996	7.74
1997	7.87
1998	7.99
1999	8.12
2000	8.25
2001	8.38
2002	8.51
2003	8.64
2004	8.78
2005	8.91
2006	9.05
2007	9.19
2008	9.32
2009	9.46
2010	9.6
2011	9.74
2012	9.88
2013	10.02
2014	10.16
2015	10.3