Year	Years
1970	3.52
1971	3.62
1972	3.72
1973	3.83
1974	3.94
1975	4.05
1976	4.16
1977	4.28
1978	4.4
1979	4.52
1980	4.64
1981	4.77
1982	4.9
1983	5.03
1984	5.16
1985	5.3
1986	5.43
1987	5.58
1988	5.72
1989	5.87
1990	6.01
1991	6.17
1992	6.32
1993	6.47
1994	6.63
1995	6.79
1996	6.95
1997	7.12
1998	7.28
1999	7.45
2000	7.61
2001	7.78
2002	7.95
2003	8.12
2004	8.29
2005	8.46
2006	8.63
2007	8.8
2008	8.97
2009	9.14
2010	9.32
2011	9.49
2012	9.66
2013	9.83
2014	10
2015	10.18