Year	Years
1970	2.52
1971	2.59
1972	2.66
1973	2.73
1974	2.81
1975	2.88
1976	2.96
1977	3.04
1978	3.12
1979	3.2
1980	3.28
1981	3.36
1982	3.44
1983	3.53
1984	3.61
1985	3.7
1986	3.79
1987	3.87
1988	3.96
1989	4.05
1990	4.14
1991	4.23
1992	4.32
1993	4.41
1994	4.5
1995	4.59
1996	4.69
1997	4.8
1998	4.91
1999	5.02
2000	5.14
2001	5.25
2002	5.37
2003	5.49
2004	5.62
2005	5.75
2006	5.87
2007	6
2008	6.14
2009	6.27
2010	6.41
2011	6.55
2012	6.69
2013	6.84
2014	6.98
2015	7.13