Year	Years
1970	2.69
1971	2.75
1972	2.82
1973	2.89
1974	2.96
1975	3.03
1976	3.11
1977	3.18
1978	3.26
1979	3.34
1980	3.41
1981	3.5
1982	3.58
1983	3.66
1984	3.75
1985	3.83
1986	3.92
1987	4.01
1988	4.1
1989	4.19
1990	4.29
1991	4.38
1992	4.48
1993	4.58
1994	4.68
1995	4.78
1996	4.88
1997	4.99
1998	5.09
1999	5.2
2000	5.31
2001	5.42
2002	5.53
2003	5.64
2004	5.76
2005	5.87
2006	5.99
2007	6.11
2008	6.23
2009	6.35
2010	6.47
2011	6.59
2012	6.72
2013	6.84
2014	6.97
2015	7.09