Year	Years
1970	2.49
1971	2.57
1972	2.65
1973	2.73
1974	2.82
1975	2.9
1976	2.99
1977	3.09
1978	3.18
1979	3.28
1980	3.38
1981	3.48
1982	3.58
1983	3.69
1984	3.8
1985	3.91
1986	4.03
1987	4.15
1988	4.27
1989	4.4
1990	4.52
1991	4.65
1992	4.79
1993	4.92
1994	5.06
1995	5.2
1996	5.34
1997	5.48
1998	5.62
1999	5.76
2000	5.9
2001	6.04
2002	6.19
2003	6.34
2004	6.49
2005	6.64
2006	6.79
2007	6.94
2008	7.1
2009	7.25
2010	7.41
2011	7.57
2012	7.73
2013	7.89
2014	8.05
2015	8.22