Year	Years
1970	2.42
1971	2.5
1972	2.57
1973	2.65
1974	2.73
1975	2.81
1976	2.89
1977	2.97
1978	3.06
1979	3.15
1980	3.24
1981	3.33
1982	3.43
1983	3.53
1984	3.63
1985	3.73
1986	3.83
1987	3.94
1988	4.05
1989	4.16
1990	4.28
1991	4.4
1992	4.52
1993	4.64
1994	4.77
1995	4.9
1996	5.03
1997	5.17
1998	5.3
1999	5.44
2000	5.58
2001	5.73
2002	5.87
2003	6.02
2004	6.17
2005	6.32
2006	6.47
2007	6.62
2008	6.78
2009	6.93
2010	7.09
2011	7.25
2012	7.41
2013	7.57
2014	7.73
2015	7.89