Year	Years
1970	2.71
1971	2.78
1972	2.84
1973	2.91
1974	2.97
1975	3.04
1976	3.11
1977	3.18
1978	3.25
1979	3.32
1980	3.4
1981	3.47
1982	3.55
1983	3.62
1984	3.7
1985	3.78
1986	3.86
1987	3.94
1988	4.02
1989	4.1
1990	4.19
1991	4.27
1992	4.36
1993	4.44
1994	4.53
1995	4.62
1996	4.71
1997	4.8
1998	4.89
1999	4.99
2000	5.09
2001	5.19
2002	5.29
2003	5.39
2004	5.5
2005	5.6
2006	5.71
2007	5.82
2008	5.94
2009	6.05
2010	6.17
2011	6.29
2012	6.41
2013	6.53
2014	6.66
2015	6.79