Year	Years
1970	2.62
1971	2.69
1972	2.75
1973	2.82
1974	2.88
1975	2.95
1976	3.02
1977	3.09
1978	3.16
1979	3.23
1980	3.3
1981	3.38
1982	3.45
1983	3.53
1984	3.61
1985	3.69
1986	3.77
1987	3.85
1988	3.93
1989	4.01
1990	4.1
1991	4.18
1992	4.27
1993	4.36
1994	4.45
1995	4.54
1996	4.64
1997	4.73
1998	4.83
1999	4.94
2000	5.04
2001	5.15
2002	5.25
2003	5.36
2004	5.47
2005	5.58
2006	5.69
2007	5.81
2008	5.92
2009	6.04
2010	6.16
2011	6.28
2012	6.4
2013	6.52
2014	6.64
2015	6.77