Year	Years
1970	4.84
1971	4.93
1972	5.03
1973	5.13
1974	5.24
1975	5.34
1976	5.44
1977	5.55
1978	5.65
1979	5.76
1980	5.87
1981	5.98
1982	6.09
1983	6.2
1984	6.32
1985	6.43
1986	6.55
1987	6.67
1988	6.78
1989	6.91
1990	7.03
1991	7.15
1992	7.28
1993	7.4
1994	7.53
1995	7.66
1996	7.8
1997	7.94
1998	8.08
1999	8.22
2000	8.36
2001	8.51
2002	8.65
2003	8.79
2004	8.93
2005	9.08
2006	9.22
2007	9.37
2008	9.51
2009	9.66
2010	9.8
2011	9.95
2012	10.09
2013	10.24
2014	10.38
2015	10.52