Year	Years
1970	2.55
1971	2.62
1972	2.68
1973	2.75
1974	2.82
1975	2.89
1976	2.96
1977	3.03
1978	3.1
1979	3.18
1980	3.25
1981	3.33
1982	3.41
1983	3.49
1984	3.57
1985	3.66
1986	3.74
1987	3.83
1988	3.92
1989	4.01
1990	4.1
1991	4.2
1992	4.3
1993	4.39
1994	4.49
1995	4.59
1996	4.7
1997	4.81
1998	4.91
1999	5.02
2000	5.13
2001	5.24
2002	5.36
2003	5.47
2004	5.58
2005	5.7
2006	5.82
2007	5.94
2008	6.06
2009	6.18
2010	6.3
2011	6.42
2012	6.55
2013	6.67
2014	6.8
2015	6.93