Year	Years
1970	3.03
1971	3.12
1972	3.21
1973	3.3
1974	3.4
1975	3.49
1976	3.6
1977	3.7
1978	3.81
1979	3.92
1980	4.03
1981	4.15
1982	4.27
1983	4.39
1984	4.52
1985	4.65
1986	4.79
1987	4.93
1988	5.07
1989	5.22
1990	5.37
1991	5.53
1992	5.68
1993	5.85
1994	6.01
1995	6.17
1996	6.32
1997	6.46
1998	6.6
1999	6.74
2000	6.88
2001	7.03
2002	7.17
2003	7.31
2004	7.45
2005	7.59
2006	7.73
2007	7.87
2008	8.01
2009	8.15
2010	8.3
2011	8.44
2012	8.58
2013	8.72
2014	8.86
2015	9