Year	Years
1970	2.67
1971	2.73
1972	2.8
1973	2.87
1974	2.94
1975	3.01
1976	3.08
1977	3.15
1978	3.23
1979	3.3
1980	3.38
1981	3.46
1982	3.54
1983	3.62
1984	3.71
1985	3.79
1986	3.87
1987	3.96
1988	4.05
1989	4.14
1990	4.23
1991	4.32
1992	4.41
1993	4.5
1994	4.59
1995	4.69
1996	4.78
1997	4.88
1998	4.98
1999	5.08
2000	5.18
2001	5.28
2002	5.39
2003	5.49
2004	5.6
2005	5.71
2006	5.82
2007	5.93
2008	6.05
2009	6.16
2010	6.28
2011	6.4
2012	6.52
2013	6.64
2014	6.76
2015	6.88