Year	Years
1970	2.77
1971	2.85
1972	2.95
1973	3.04
1974	3.14
1975	3.24
1976	3.34
1977	3.45
1978	3.56
1979	3.68
1980	3.79
1981	3.91
1982	4.04
1983	4.17
1984	4.3
1985	4.43
1986	4.57
1987	4.72
1988	4.87
1989	5.02
1990	5.18
1991	5.34
1992	5.5
1993	5.68
1994	5.85
1995	6.03
1996	6.22
1997	6.4
1998	6.59
1999	6.77
2000	6.95
2001	7.14
2002	7.32
2003	7.5
2004	7.68
2005	7.86
2006	8.04
2007	8.22
2008	8.39
2009	8.57
2010	8.74
2011	8.92
2012	9.09
2013	9.26
2014	9.44
2015	9.61