Year	Years
1970	2.54
1971	2.62
1972	2.69
1973	2.77
1974	2.85
1975	2.94
1976	3.02
1977	3.11
1978	3.2
1979	3.29
1980	3.38
1981	3.48
1982	3.57
1983	3.67
1984	3.77
1985	3.88
1986	3.98
1987	4.09
1988	4.2
1989	4.31
1990	4.42
1991	4.54
1992	4.66
1993	4.78
1994	4.9
1995	5.02
1996	5.15
1997	5.27
1998	5.4
1999	5.52
2000	5.66
2001	5.79
2002	5.92
2003	6.06
2004	6.2
2005	6.34
2006	6.49
2007	6.63
2008	6.78
2009	6.93
2010	7.08
2011	7.23
2012	7.38
2013	7.54
2014	7.69
2015	7.85