Year	Years
1970	4.99
1971	5.09
1972	5.19
1973	5.29
1974	5.39
1975	5.49
1976	5.59
1977	5.7
1978	5.8
1979	5.9
1980	6.01
1981	6.11
1982	6.22
1983	6.32
1984	6.42
1985	6.52
1986	6.62
1987	6.72
1988	6.82
1989	6.92
1990	7.01
1991	7.11
1992	7.2
1993	7.28
1994	7.37
1995	7.45
1996	7.56
1997	7.66
1998	7.77
1999	7.89
2000	8
2001	8.12
2002	8.24
2003	8.36
2004	8.49
2005	8.61
2006	8.74
2007	8.87
2008	9
2009	9.13
2010	9.26
2011	9.39
2012	9.53
2013	9.66
2014	9.8
2015	9.93