Year	Years
1970	4.43
1971	4.53
1972	4.63
1973	4.74
1974	4.84
1975	4.95
1976	5.06
1977	5.17
1978	5.29
1979	5.4
1980	5.52
1981	5.64
1982	5.76
1983	5.88
1984	6
1985	6.12
1986	6.25
1987	6.38
1988	6.5
1989	6.63
1990	6.76
1991	6.89
1992	7.02
1993	7.16
1994	7.29
1995	7.42
1996	7.55
1997	7.67
1998	7.8
1999	7.93
2000	8.06
2001	8.19
2002	8.32
2003	8.46
2004	8.59
2005	8.72
2006	8.86
2007	8.99
2008	9.13
2009	9.26
2010	9.4
2011	9.53
2012	9.67
2013	9.81
2014	9.94
2015	10.08