Year	Years
1970	2.76
1971	2.82
1972	2.89
1973	2.96
1974	3.03
1975	3.1
1976	3.18
1977	3.25
1978	3.33
1979	3.4
1980	3.48
1981	3.57
1982	3.65
1983	3.73
1984	3.82
1985	3.91
1986	4
1987	4.09
1988	4.18
1989	4.28
1990	4.38
1991	4.47
1992	4.58
1993	4.68
1994	4.79
1995	4.9
1996	5.01
1997	5.13
1998	5.24
1999	5.36
2000	5.48
2001	5.61
2002	5.73
2003	5.85
2004	5.98
2005	6.11
2006	6.23
2007	6.36
2008	6.49
2009	6.63
2010	6.76
2011	6.89
2012	7.03
2013	7.16
2014	7.3
2015	7.43