Year	Years
1970	2.2
1971	2.27
1972	2.35
1973	2.42
1974	2.5
1975	2.58
1976	2.67
1977	2.75
1978	2.84
1979	2.93
1980	3.02
1981	3.12
1982	3.22
1983	3.32
1984	3.42
1985	3.53
1986	3.64
1987	3.75
1988	3.87
1989	3.98
1990	4.11
1991	4.23
1992	4.36
1993	4.49
1994	4.62
1995	4.76
1996	4.9
1997	5.04
1998	5.19
1999	5.33
2000	5.48
2001	5.63
2002	5.78
2003	5.93
2004	6.08
2005	6.23
2006	6.39
2007	6.54
2008	6.7
2009	6.85
2010	7.01
2011	7.16
2012	7.32
2013	7.48
2014	7.64
2015	7.8