Year	Years
1970	3.38
1971	3.48
1972	3.59
1973	3.69
1974	3.8
1975	3.91
1976	4.03
1977	4.15
1978	4.27
1979	4.39
1980	4.52
1981	4.65
1982	4.78
1983	4.92
1984	5.06
1985	5.2
1986	5.35
1987	5.5
1988	5.65
1989	5.81
1990	5.97
1991	6.13
1992	6.3
1993	6.47
1994	6.65
1995	6.83
1996	7
1997	7.18
1998	7.35
1999	7.52
2000	7.7
2001	7.87
2002	8.05
2003	8.22
2004	8.4
2005	8.57
2006	8.75
2007	8.92
2008	9.1
2009	9.27
2010	9.45
2011	9.62
2012	9.8
2013	9.97
2014	10.14
2015	10.32