Year	Years
1970	2.86
1971	2.96
1972	3.06
1973	3.17
1974	3.28
1975	3.4
1976	3.52
1977	3.65
1978	3.79
1979	3.93
1980	4.07
1981	4.23
1982	4.39
1983	4.55
1984	4.73
1985	4.91
1986	5.1
1987	5.3
1988	5.5
1989	5.72
1990	5.94
1991	6.17
1992	6.4
1993	6.64
1994	6.88
1995	7.12
1996	7.28
1997	7.44
1998	7.59
1999	7.74
2000	7.89
2001	8.04
2002	8.19
2003	8.34
2004	8.48
2005	8.63
2006	8.77
2007	8.91
2008	9.06
2009	9.2
2010	9.34
2011	9.48
2012	9.62
2013	9.76
2014	9.9
2015	10.04