Year	Years
1970	4.43
1971	4.53
1972	4.63
1973	4.73
1974	4.83
1975	4.93
1976	5.04
1977	5.14
1978	5.25
1979	5.36
1980	5.47
1981	5.58
1982	5.7
1983	5.81
1984	5.93
1985	6.04
1986	6.16
1987	6.28
1988	6.4
1989	6.52
1990	6.65
1991	6.77
1992	6.9
1993	7.02
1994	7.15
1995	7.28
1996	7.4
1997	7.53
1998	7.66
1999	7.8
2000	7.93
2001	8.06
2002	8.2
2003	8.33
2004	8.46
2005	8.6
2006	8.74
2007	8.87
2008	9.01
2009	9.15
2010	9.28
2011	9.42
2012	9.56
2013	9.7
2014	9.84
2015	9.98