Year	Years
1970	2.81
1971	2.89
1972	2.97
1973	3.05
1974	3.13
1975	3.22
1976	3.31
1977	3.39
1978	3.48
1979	3.58
1980	3.67
1981	3.77
1982	3.86
1983	3.97
1984	4.07
1985	4.18
1986	4.29
1987	4.4
1988	4.52
1989	4.64
1990	4.76
1991	4.89
1992	5.03
1993	5.17
1994	5.32
1995	5.47
1996	5.64
1997	5.82
1998	5.99
1999	6.16
2000	6.33
2001	6.5
2002	6.67
2003	6.85
2004	7.02
2005	7.19
2006	7.37
2007	7.54
2008	7.71
2009	7.89
2010	8.06
2011	8.23
2012	8.41
2013	8.58
2014	8.75
2015	8.92