Year	Years
1970	5.61
1971	5.71
1972	5.8
1973	5.9
1974	5.99
1975	6.08
1976	6.17
1977	6.26
1978	6.35
1979	6.44
1980	6.52
1981	6.6
1982	6.68
1983	6.76
1984	6.83
1985	6.9
1986	6.96
1987	7.02
1988	7.08
1989	7.13
1990	7.17
1991	7.2
1992	7.23
1993	7.25
1994	7.27
1995	7.28
1996	7.37
1997	7.46
1998	7.56
1999	7.66
2000	7.76
2001	7.87
2002	7.98
2003	8.09
2004	8.21
2005	8.33
2006	8.45
2007	8.57
2008	8.7
2009	8.82
2010	8.95
2011	9.08
2012	9.21
2013	9.34
2014	9.47
2015	9.6