Year	Years
1970	2.52
1971	2.6
1972	2.68
1973	2.76
1974	2.85
1975	2.93
1976	3.02
1977	3.12
1978	3.21
1979	3.31
1980	3.41
1981	3.51
1982	3.62
1983	3.73
1984	3.84
1985	3.96
1986	4.07
1987	4.19
1988	4.32
1989	4.45
1990	4.58
1991	4.71
1992	4.85
1993	4.99
1994	5.14
1995	5.28
1996	5.43
1997	5.58
1998	5.73
1999	5.88
2000	6.03
2001	6.19
2002	6.34
2003	6.5
2004	6.65
2005	6.81
2006	6.97
2007	7.13
2008	7.29
2009	7.46
2010	7.62
2011	7.79
2012	7.95
2013	8.12
2014	8.28
2015	8.45