Year	Years
1970	4.44
1971	4.54
1972	4.64
1973	4.74
1974	4.85
1975	4.96
1976	5.06
1977	5.17
1978	5.29
1979	5.4
1980	5.51
1981	5.63
1982	5.75
1983	5.87
1984	5.99
1985	6.11
1986	6.23
1987	6.36
1988	6.49
1989	6.61
1990	6.74
1991	6.87
1992	7
1993	7.13
1994	7.27
1995	7.4
1996	7.53
1997	7.66
1998	7.79
1999	7.92
2000	8.05
2001	8.19
2002	8.32
2003	8.45
2004	8.59
2005	8.73
2006	8.86
2007	9
2008	9.13
2009	9.27
2010	9.41
2011	9.55
2012	9.69
2013	9.82
2014	9.96
2015	10.1