Year	Years
1970	2.97
1971	3.05
1972	3.12
1973	3.2
1974	3.27
1975	3.35
1976	3.43
1977	3.51
1978	3.6
1979	3.68
1980	3.77
1981	3.85
1982	3.94
1983	4.03
1984	4.12
1985	4.22
1986	4.31
1987	4.41
1988	4.5
1989	4.6
1990	4.7
1991	4.8
1992	4.9
1993	5.01
1994	5.11
1995	5.22
1996	5.32
1997	5.43
1998	5.54
1999	5.65
2000	5.76
2001	5.87
2002	5.98
2003	6.09
2004	6.21
2005	6.33
2006	6.44
2007	6.56
2008	6.68
2009	6.81
2010	6.93
2011	7.05
2012	7.18
2013	7.3
2014	7.43
2015	7.56