Year	Years
1970	4.19
1971	4.3
1972	4.41
1973	4.53
1974	4.64
1975	4.76
1976	4.89
1977	5.01
1978	5.14
1979	5.27
1980	5.4
1981	5.54
1982	5.68
1983	5.82
1984	5.96
1985	6.1
1986	6.25
1987	6.39
1988	6.54
1989	6.69
1990	6.84
1991	6.99
1992	7.14
1993	7.29
1994	7.44
1995	7.59
1996	7.71
1997	7.84
1998	7.97
1999	8.09
2000	8.22
2001	8.34
2002	8.47
2003	8.59
2004	8.71
2005	8.84
2006	8.96
2007	9.08
2008	9.21
2009	9.33
2010	9.46
2011	9.58
2012	9.71
2013	9.83
2014	9.96
2015	10.09