Year	Years
1970	4.89
1971	4.99
1972	5.09
1973	5.2
1974	5.3
1975	5.41
1976	5.51
1977	5.62
1978	5.73
1979	5.84
1980	5.95
1981	6.06
1982	6.17
1983	6.28
1984	6.39
1985	6.5
1986	6.61
1987	6.72
1988	6.83
1989	6.94
1990	7.05
1991	7.16
1992	7.26
1993	7.37
1994	7.48
1995	7.58
1996	7.69
1997	7.79
1998	7.9
1999	8.02
2000	8.13
2001	8.25
2002	8.36
2003	8.48
2004	8.6
2005	8.72
2006	8.85
2007	8.97
2008	9.09
2009	9.22
2010	9.35
2011	9.48
2012	9.61
2013	9.74
2014	9.87
2015	10