Year	Years
1970	2.64
1971	2.7
1972	2.77
1973	2.84
1974	2.91
1975	2.98
1976	3.05
1977	3.12
1978	3.2
1979	3.27
1980	3.35
1981	3.43
1982	3.51
1983	3.59
1984	3.67
1985	3.76
1986	3.84
1987	3.93
1988	4.02
1989	4.11
1990	4.2
1991	4.3
1992	4.39
1993	4.49
1994	4.59
1995	4.69
1996	4.79
1997	4.89
1998	4.99
1999	5.1
2000	5.2
2001	5.31
2002	5.42
2003	5.53
2004	5.64
2005	5.76
2006	5.87
2007	5.99
2008	6.11
2009	6.22
2010	6.35
2011	6.47
2012	6.59
2013	6.71
2014	6.84
2015	6.97