Year	Years
1970	3.3
1971	3.38
1972	3.46
1973	3.54
1974	3.63
1975	3.71
1976	3.8
1977	3.89
1978	3.98
1979	4.07
1980	4.17
1981	4.26
1982	4.36
1983	4.46
1984	4.56
1985	4.67
1986	4.77
1987	4.88
1988	4.98
1989	5.09
1990	5.2
1991	5.32
1992	5.43
1993	5.55
1994	5.67
1995	5.79
1996	5.91
1997	6.03
1998	6.16
1999	6.28
2000	6.41
2001	6.54
2002	6.67
2003	6.79
2004	6.93
2005	7.06
2006	7.19
2007	7.32
2008	7.46
2009	7.59
2010	7.73
2011	7.86
2012	8
2013	8.14
2014	8.27
2015	8.41