Year	Years
1970	4.55
1971	4.66
1972	4.78
1973	4.9
1974	5.01
1975	5.13
1976	5.25
1977	5.37
1978	5.49
1979	5.61
1980	5.73
1981	5.85
1982	5.97
1983	6.09
1984	6.2
1985	6.32
1986	6.43
1987	6.55
1988	6.66
1989	6.77
1990	6.87
1991	6.97
1992	7.07
1993	7.16
1994	7.25
1995	7.33
1996	7.45
1997	7.57
1998	7.7
1999	7.82
2000	7.96
2001	8.09
2002	8.23
2003	8.37
2004	8.52
2005	8.66
2006	8.81
2007	8.96
2008	9.12
2009	9.27
2010	9.43
2011	9.59
2012	9.74
2013	9.9
2014	10.06
2015	10.23