Year	Years
1970	2.94
1971	3
1972	3.06
1973	3.12
1974	3.18
1975	3.24
1976	3.3
1977	3.36
1978	3.43
1979	3.49
1980	3.55
1981	3.61
1982	3.67
1983	3.73
1984	3.79
1985	3.85
1986	3.91
1987	3.97
1988	4.03
1989	4.08
1990	4.14
1991	4.19
1992	4.25
1993	4.3
1994	4.35
1995	4.4
1996	4.47
1997	4.54
1998	4.62
1999	4.7
2000	4.78
2001	4.86
2002	4.94
2003	5.03
2004	5.12
2005	5.21
2006	5.31
2007	5.4
2008	5.5
2009	5.6
2010	5.7
2011	5.81
2012	5.91
2013	6.02
2014	6.13
2015	6.24