Year	Years
1970	2.82
1971	2.89
1972	2.96
1973	3.03
1974	3.11
1975	3.18
1976	3.26
1977	3.34
1978	3.42
1979	3.51
1980	3.59
1981	3.68
1982	3.76
1983	3.85
1984	3.94
1985	4.03
1986	4.13
1987	4.22
1988	4.32
1989	4.42
1990	4.52
1991	4.62
1992	4.72
1993	4.82
1994	4.93
1995	5.03
1996	5.14
1997	5.25
1998	5.37
1999	5.48
2000	5.6
2001	5.71
2002	5.83
2003	5.95
2004	6.07
2005	6.19
2006	6.31
2007	6.44
2008	6.56
2009	6.69
2010	6.81
2011	6.94
2012	7.07
2013	7.19
2014	7.32
2015	7.45