Year	Years
1970	4.76
1971	4.86
1972	4.97
1973	5.07
1974	5.18
1975	5.29
1976	5.4
1977	5.51
1978	5.62
1979	5.73
1980	5.84
1981	5.96
1982	6.07
1983	6.18
1984	6.3
1985	6.41
1986	6.53
1987	6.65
1988	6.76
1989	6.87
1990	6.99
1991	7.1
1992	7.21
1993	7.32
1994	7.43
1995	7.54
1996	7.65
1997	7.75
1998	7.86
1999	7.96
2000	8.07
2001	8.18
2002	8.29
2003	8.4
2004	8.51
2005	8.62
2006	8.73
2007	8.85
2008	8.96
2009	9.08
2010	9.2
2011	9.32
2012	9.45
2013	9.57
2014	9.7
2015	9.83