Year	Years
1970	2.86
1971	2.93
1972	3
1973	3.07
1974	3.14
1975	3.22
1976	3.29
1977	3.37
1978	3.45
1979	3.53
1980	3.61
1981	3.69
1982	3.77
1983	3.86
1984	3.94
1985	4.03
1986	4.12
1987	4.21
1988	4.3
1989	4.39
1990	4.48
1991	4.58
1992	4.68
1993	4.77
1994	4.87
1995	4.97
1996	5.07
1997	5.18
1998	5.28
1999	5.39
2000	5.49
2001	5.6
2002	5.71
2003	5.82
2004	5.94
2005	6.05
2006	6.17
2007	6.29
2008	6.41
2009	6.53
2010	6.65
2011	6.77
2012	6.9
2013	7.03
2014	7.16
2015	7.29