Year	Years
1970	3.65
1971	3.75
1972	3.86
1973	3.96
1974	4.07
1975	4.18
1976	4.29
1977	4.41
1978	4.52
1979	4.64
1980	4.76
1981	4.88
1982	5
1983	5.13
1984	5.25
1985	5.38
1986	5.51
1987	5.64
1988	5.77
1989	5.9
1990	6.03
1991	6.17
1992	6.3
1993	6.43
1994	6.57
1995	6.7
1996	6.83
1997	6.96
1998	7.09
1999	7.23
2000	7.36
2001	7.5
2002	7.64
2003	7.78
2004	7.93
2005	8.07
2006	8.22
2007	8.37
2008	8.52
2009	8.67
2010	8.82
2011	8.98
2012	9.13
2013	9.29
2014	9.45
2015	9.61