Year	Years
1970	4.46
1971	4.58
1972	4.7
1973	4.83
1974	4.95
1975	5.08
1976	5.21
1977	5.33
1978	5.46
1979	5.6
1980	5.73
1981	5.86
1982	5.99
1983	6.12
1984	6.26
1985	6.39
1986	6.52
1987	6.65
1988	6.78
1989	6.91
1990	7.03
1991	7.15
1992	7.27
1993	7.39
1994	7.51
1995	7.62
1996	7.71
1997	7.81
1998	7.9
1999	8.01
2000	8.11
2001	8.22
2002	8.33
2003	8.44
2004	8.55
2005	8.67
2006	8.79
2007	8.91
2008	9.04
2009	9.17
2010	9.3
2011	9.43
2012	9.57
2013	9.71
2014	9.85
2015	10