Year	Years
1970	4.2
1971	4.3
1972	4.39
1973	4.49
1974	4.59
1975	4.7
1976	4.8
1977	4.91
1978	5.01
1979	5.12
1980	5.23
1981	5.34
1982	5.46
1983	5.57
1984	5.68
1985	5.8
1986	5.92
1987	6.04
1988	6.16
1989	6.28
1990	6.4
1991	6.52
1992	6.64
1993	6.77
1994	6.89
1995	7.02
1996	7.14
1997	7.26
1998	7.39
1999	7.51
2000	7.64
2001	7.77
2002	7.9
2003	8.02
2004	8.15
2005	8.28
2006	8.41
2007	8.54
2008	8.67
2009	8.8
2010	8.93
2011	9.06
2012	9.2
2013	9.33
2014	9.46
2015	9.6