Year	Years
1970	5.02
1971	5.12
1972	5.22
1973	5.32
1974	5.42
1975	5.52
1976	5.63
1977	5.73
1978	5.83
1979	5.93
1980	6.03
1981	6.14
1982	6.24
1983	6.34
1984	6.44
1985	6.54
1986	6.63
1987	6.73
1988	6.83
1989	6.92
1990	7.02
1991	7.11
1992	7.2
1993	7.28
1994	7.37
1995	7.45
1996	7.53
1997	7.62
1998	7.7
1999	7.8
2000	7.9
2001	7.99
2002	8.1
2003	8.2
2004	8.31
2005	8.42
2006	8.53
2007	8.64
2008	8.76
2009	8.87
2010	8.99
2011	9.11
2012	9.23
2013	9.36
2014	9.48
2015	9.61