Year	Years
1970	3.96
1971	4.05
1972	4.14
1973	4.24
1974	4.33
1975	4.43
1976	4.53
1977	4.62
1978	4.73
1979	4.83
1980	4.93
1981	5.04
1982	5.14
1983	5.25
1984	5.36
1985	5.47
1986	5.58
1987	5.69
1988	5.81
1989	5.93
1990	6.04
1991	6.16
1992	6.28
1993	6.4
1994	6.52
1995	6.65
1996	6.77
1997	6.9
1998	7.03
1999	7.15
2000	7.28
2001	7.41
2002	7.54
2003	7.67
2004	7.81
2005	7.94
2006	8.07
2007	8.21
2008	8.34
2009	8.48
2010	8.61
2011	8.75
2012	8.89
2013	9.02
2014	9.16
2015	9.3