Year	Years
1970	2.72
1971	2.79
1972	2.85
1973	2.92
1974	2.99
1975	3.07
1976	3.14
1977	3.21
1978	3.29
1979	3.37
1980	3.45
1981	3.53
1982	3.61
1983	3.7
1984	3.78
1985	3.87
1986	3.96
1987	4.05
1988	4.14
1989	4.24
1990	4.33
1991	4.43
1992	4.53
1993	4.63
1994	4.74
1995	4.84
1996	4.96
1997	5.07
1998	5.18
1999	5.3
2000	5.41
2001	5.53
2002	5.65
2003	5.77
2004	5.89
2005	6.02
2006	6.14
2007	6.27
2008	6.4
2009	6.52
2010	6.65
2011	6.78
2012	6.91
2013	7.05
2014	7.18
2015	7.31