Year	Years
1970	4.77
1971	4.86
1972	4.94
1973	5.02
1974	5.11
1975	5.19
1976	5.27
1977	5.35
1978	5.43
1979	5.51
1980	5.58
1981	5.66
1982	5.74
1983	5.81
1984	5.88
1985	5.96
1986	6.03
1987	6.1
1988	6.17
1989	6.24
1990	6.3
1991	6.37
1992	6.43
1993	6.5
1994	6.56
1995	6.62
1996	6.72
1997	6.82
1998	6.93
1999	7.04
2000	7.14
2001	7.25
2002	7.37
2003	7.48
2004	7.6
2005	7.72
2006	7.84
2007	7.96
2008	8.09
2009	8.21
2010	8.34
2011	8.46
2012	8.59
2013	8.72
2014	8.85
2015	8.98