Year	Years
1970	2.99
1971	3.08
1972	3.18
1973	3.27
1974	3.37
1975	3.47
1976	3.58
1977	3.69
1978	3.8
1979	3.91
1980	4.03
1981	4.14
1982	4.27
1983	4.39
1984	4.52
1985	4.65
1986	4.79
1987	4.93
1988	5.07
1989	5.21
1990	5.36
1991	5.52
1992	5.67
1993	5.84
1994	6
1995	6.17
1996	6.35
1997	6.53
1998	6.7
1999	6.88
2000	7.06
2001	7.24
2002	7.42
2003	7.6
2004	7.78
2005	7.95
2006	8.13
2007	8.31
2008	8.49
2009	8.67
2010	8.85
2011	9.02
2012	9.2
2013	9.38
2014	9.55
2015	9.73