Year	Years
1970	3.48
1971	3.59
1972	3.69
1973	3.8
1974	3.91
1975	4.02
1976	4.13
1977	4.25
1978	4.37
1979	4.48
1980	4.6
1981	4.73
1982	4.85
1983	4.98
1984	5.1
1985	5.23
1986	5.36
1987	5.48
1988	5.61
1989	5.74
1990	5.87
1991	6
1992	6.12
1993	6.25
1994	6.37
1995	6.5
1996	6.61
1997	6.72
1998	6.84
1999	6.95
2000	7.07
2001	7.19
2002	7.32
2003	7.44
2004	7.57
2005	7.7
2006	7.83
2007	7.96
2008	8.09
2009	8.23
2010	8.36
2011	8.5
2012	8.64
2013	8.79
2014	8.93
2015	9.08