Year	Years
1970	2.78
1971	2.85
1972	2.92
1973	2.99
1974	3.06
1975	3.14
1976	3.21
1977	3.29
1978	3.37
1979	3.45
1980	3.53
1981	3.62
1982	3.7
1983	3.79
1984	3.88
1985	3.97
1986	4.07
1987	4.16
1988	4.26
1989	4.36
1990	4.46
1991	4.56
1992	4.67
1993	4.77
1994	4.88
1995	4.99
1996	5.1
1997	5.22
1998	5.33
1999	5.45
2000	5.57
2001	5.69
2002	5.81
2003	5.93
2004	6.05
2005	6.17
2006	6.29
2007	6.42
2008	6.55
2009	6.67
2010	6.8
2011	6.93
2012	7.06
2013	7.19
2014	7.32
2015	7.45