Year	Years
1970	2.69
1971	2.75
1972	2.82
1973	2.89
1974	2.96
1975	3.04
1976	3.11
1977	3.19
1978	3.26
1979	3.34
1980	3.42
1981	3.51
1982	3.59
1983	3.68
1984	3.76
1985	3.85
1986	3.94
1987	4.03
1988	4.13
1989	4.22
1990	4.32
1991	4.42
1992	4.52
1993	4.62
1994	4.72
1995	4.83
1996	4.93
1997	5.04
1998	5.15
1999	5.26
2000	5.37
2001	5.49
2002	5.6
2003	5.72
2004	5.83
2005	5.95
2006	6.07
2007	6.19
2008	6.31
2009	6.43
2010	6.56
2011	6.68
2012	6.81
2013	6.93
2014	7.06
2015	7.19