Year	Years
1970	2.89
1971	2.96
1972	3.03
1973	3.11
1974	3.19
1975	3.27
1976	3.35
1977	3.43
1978	3.52
1979	3.6
1980	3.69
1981	3.77
1982	3.86
1983	3.95
1984	4.04
1985	4.13
1986	4.23
1987	4.32
1988	4.41
1989	4.51
1990	4.6
1991	4.7
1992	4.79
1993	4.89
1994	4.98
1995	5.08
1996	5.16
1997	5.25
1998	5.34
1999	5.43
2000	5.53
2001	5.62
2002	5.72
2003	5.81
2004	5.91
2005	6.01
2006	6.11
2007	6.21
2008	6.32
2009	6.42
2010	6.53
2011	6.63
2012	6.74
2013	6.85
2014	6.96
2015	7.08