Year	Years
1970	2.65
1971	2.71
1972	2.78
1973	2.85
1974	2.92
1975	2.99
1976	3.06
1977	3.14
1978	3.21
1979	3.29
1980	3.37
1981	3.45
1982	3.53
1983	3.61
1984	3.69
1985	3.78
1986	3.86
1987	3.95
1988	4.04
1989	4.13
1990	4.22
1991	4.32
1992	4.41
1993	4.51
1994	4.6
1995	4.7
1996	4.8
1997	4.9
1998	5.01
1999	5.11
2000	5.22
2001	5.32
2002	5.43
2003	5.54
2004	5.65
2005	5.76
2006	5.88
2007	5.99
2008	6.11
2009	6.23
2010	6.35
2011	6.47
2012	6.59
2013	6.71
2014	6.84
2015	6.96