Year	Years
1970	4.05
1971	4.16
1972	4.26
1973	4.37
1974	4.48
1975	4.59
1976	4.7
1977	4.82
1978	4.93
1979	5.05
1980	5.16
1981	5.28
1982	5.4
1983	5.52
1984	5.64
1985	5.76
1986	5.89
1987	6.01
1988	6.13
1989	6.25
1990	6.38
1991	6.5
1992	6.62
1993	6.75
1994	6.87
1995	6.99
1996	7.13
1997	7.27
1998	7.41
1999	7.55
2000	7.7
2001	7.84
2002	7.99
2003	8.15
2004	8.3
2005	8.45
2006	8.61
2007	8.77
2008	8.93
2009	9.09
2010	9.25
2011	9.41
2012	9.57
2013	9.73
2014	9.9
2015	10.06