Year	Years
1970	4.68
1971	4.77
1972	4.87
1973	4.97
1974	5.07
1975	5.17
1976	5.27
1977	5.37
1978	5.47
1979	5.57
1980	5.68
1981	5.78
1982	5.88
1983	5.99
1984	6.09
1985	6.2
1986	6.3
1987	6.41
1988	6.51
1989	6.62
1990	6.72
1991	6.83
1992	6.93
1993	7.03
1994	7.14
1995	7.24
1996	7.35
1997	7.46
1998	7.58
1999	7.69
2000	7.81
2001	7.93
2002	8.05
2003	8.18
2004	8.3
2005	8.43
2006	8.55
2007	8.68
2008	8.81
2009	8.94
2010	9.07
2011	9.21
2012	9.34
2013	9.47
2014	9.61
2015	9.74