Year	Years
1970	4.9
1971	5.01
1972	5.12
1973	5.23
1974	5.34
1975	5.45
1976	5.57
1977	5.68
1978	5.8
1979	5.91
1980	6.03
1981	6.15
1982	6.27
1983	6.39
1984	6.51
1985	6.64
1986	6.76
1987	6.88
1988	7
1989	7.12
1990	7.24
1991	7.36
1992	7.48
1993	7.6
1994	7.72
1995	7.84
1996	7.95
1997	8.06
1998	8.17
1999	8.28
2000	8.39
2001	8.51
2002	8.62
2003	8.74
2004	8.86
2005	8.97
2006	9.09
2007	9.21
2008	9.33
2009	9.45
2010	9.58
2011	9.7
2012	9.83
2013	9.95
2014	10.08
2015	10.2