Year	Years
1970	3.64
1971	3.74
1972	3.84
1973	3.95
1974	4.05
1975	4.16
1976	4.27
1977	4.39
1978	4.5
1979	4.62
1980	4.74
1981	4.86
1982	4.98
1983	5.11
1984	5.23
1985	5.36
1986	5.49
1987	5.62
1988	5.76
1989	5.89
1990	6.03
1991	6.17
1992	6.31
1993	6.46
1994	6.6
1995	6.75
1996	6.9
1997	7.06
1998	7.21
1999	7.37
2000	7.53
2001	7.69
2002	7.85
2003	8.01
2004	8.17
2005	8.34
2006	8.5
2007	8.66
2008	8.83
2009	9
2010	9.16
2011	9.33
2012	9.5
2013	9.66
2014	9.83
2015	10