Year	Years
1970	3.72
1971	3.82
1972	3.93
1973	4.04
1974	4.15
1975	4.26
1976	4.37
1977	4.49
1978	4.61
1979	4.73
1980	4.85
1981	4.97
1982	5.1
1983	5.23
1984	5.36
1985	5.49
1986	5.62
1987	5.76
1988	5.9
1989	6.04
1990	6.18
1991	6.32
1992	6.46
1993	6.61
1994	6.76
1995	6.91
1996	7.06
1997	7.21
1998	7.36
1999	7.52
2000	7.68
2001	7.84
2002	7.99
2003	8.15
2004	8.32
2005	8.48
2006	8.64
2007	8.81
2008	8.97
2009	9.13
2010	9.3
2011	9.47
2012	9.63
2013	9.8
2014	9.97
2015	10.13