Year	Years
1970	2.65
1971	2.72
1972	2.8
1973	2.87
1974	2.95
1975	3.03
1976	3.11
1977	3.19
1978	3.28
1979	3.36
1980	3.45
1981	3.54
1982	3.62
1983	3.71
1984	3.81
1985	3.9
1986	3.99
1987	4.09
1988	4.18
1989	4.28
1990	4.38
1991	4.48
1992	4.59
1993	4.69
1994	4.8
1995	4.92
1996	5.04
1997	5.17
1998	5.31
1999	5.44
2000	5.58
2001	5.71
2002	5.85
2003	6
2004	6.14
2005	6.28
2006	6.43
2007	6.58
2008	6.73
2009	6.87
2010	7.02
2011	7.18
2012	7.33
2013	7.48
2014	7.63
2015	7.78