Year	Years
1970	4.05
1971	4.16
1972	4.26
1973	4.37
1974	4.48
1975	4.6
1976	4.71
1977	4.83
1978	4.95
1979	5.07
1980	5.2
1981	5.32
1982	5.45
1983	5.58
1984	5.71
1985	5.84
1986	5.97
1987	6.11
1988	6.24
1989	6.38
1990	6.51
1991	6.65
1992	6.79
1993	6.93
1994	7.06
1995	7.2
1996	7.34
1997	7.48
1998	7.61
1999	7.75
2000	7.89
2001	8.03
2002	8.17
2003	8.31
2004	8.45
2005	8.6
2006	8.74
2007	8.88
2008	9.02
2009	9.16
2010	9.3
2011	9.44
2012	9.58
2013	9.72
2014	9.86
2015	10