Year	Years
1970	2.72
1971	2.8
1972	2.89
1973	2.98
1974	3.07
1975	3.16
1976	3.26
1977	3.35
1978	3.45
1979	3.55
1980	3.65
1981	3.75
1982	3.86
1983	3.96
1984	4.07
1985	4.18
1986	4.29
1987	4.4
1988	4.51
1989	4.62
1990	4.73
1991	4.85
1992	4.96
1993	5.08
1994	5.2
1995	5.32
1996	5.43
1997	5.55
1998	5.67
1999	5.79
2000	5.92
2001	6.04
2002	6.16
2003	6.29
2004	6.42
2005	6.55
2006	6.68
2007	6.82
2008	6.95
2009	7.09
2010	7.23
2011	7.37
2012	7.52
2013	7.66
2014	7.81
2015	7.96