Year	Years
1970	2.97
1971	3.05
1972	3.12
1973	3.2
1974	3.28
1975	3.36
1976	3.45
1977	3.53
1978	3.62
1979	3.7
1980	3.79
1981	3.88
1982	3.98
1983	4.07
1984	4.17
1985	4.27
1986	4.36
1987	4.46
1988	4.57
1989	4.67
1990	4.77
1991	4.88
1992	4.98
1993	5.09
1994	5.19
1995	5.3
1996	5.4
1997	5.5
1998	5.61
1999	5.71
2000	5.82
2001	5.93
2002	6.04
2003	6.16
2004	6.27
2005	6.39
2006	6.5
2007	6.62
2008	6.74
2009	6.87
2010	6.99
2011	7.11
2012	7.24
2013	7.37
2014	7.49
2015	7.62