Year	Years
1970	2.43
1971	2.49
1972	2.55
1973	2.61
1974	2.68
1975	2.74
1976	2.81
1977	2.88
1978	2.95
1979	3.02
1980	3.1
1981	3.17
1982	3.25
1983	3.33
1984	3.41
1985	3.49
1986	3.57
1987	3.66
1988	3.75
1989	3.84
1990	3.93
1991	4.02
1992	4.11
1993	4.21
1994	4.31
1995	4.41
1996	4.51
1997	4.61
1998	4.72
1999	4.83
2000	4.94
2001	5.05
2002	5.16
2003	5.27
2004	5.38
2005	5.5
2006	5.61
2007	5.73
2008	5.85
2009	5.97
2010	6.09
2011	6.21
2012	6.33
2013	6.46
2014	6.58
2015	6.71