Year	Years
1970	4.43
1971	4.53
1972	4.63
1973	4.73
1974	4.83
1975	4.94
1976	5.05
1977	5.15
1978	5.26
1979	5.38
1980	5.49
1981	5.6
1982	5.72
1983	5.84
1984	5.96
1985	6.08
1986	6.2
1987	6.32
1988	6.45
1989	6.57
1990	6.7
1991	6.83
1992	6.96
1993	7.09
1994	7.22
1995	7.35
1996	7.49
1997	7.62
1998	7.75
1999	7.88
2000	8.02
2001	8.15
2002	8.29
2003	8.43
2004	8.56
2005	8.7
2006	8.84
2007	8.98
2008	9.12
2009	9.26
2010	9.4
2011	9.54
2012	9.68
2013	9.82
2014	9.96
2015	10.1