Year	Years
1970	4.76
1971	4.86
1972	4.97
1973	5.08
1974	5.19
1975	5.3
1976	5.41
1977	5.53
1978	5.64
1979	5.76
1980	5.88
1981	6
1982	6.12
1983	6.24
1984	6.36
1985	6.48
1986	6.6
1987	6.72
1988	6.85
1989	6.97
1990	7.1
1991	7.22
1992	7.35
1993	7.47
1994	7.6
1995	7.72
1996	7.84
1997	7.97
1998	8.09
1999	8.21
2000	8.34
2001	8.46
2002	8.59
2003	8.72
2004	8.84
2005	8.97
2006	9.1
2007	9.22
2008	9.35
2009	9.48
2010	9.61
2011	9.74
2012	9.87
2013	10
2014	10.13
2015	10.26