Year	Years
1970	2.75
1971	2.85
1972	2.95
1973	3.06
1974	3.17
1975	3.29
1976	3.4
1977	3.53
1978	3.66
1979	3.79
1980	3.93
1981	4.07
1982	4.22
1983	4.37
1984	4.53
1985	4.69
1986	4.86
1987	5.04
1988	5.22
1989	5.41
1990	5.6
1991	5.8
1992	6.01
1993	6.22
1994	6.43
1995	6.66
1996	6.85
1997	7.05
1998	7.25
1999	7.44
2000	7.63
2001	7.82
2002	8.01
2003	8.2
2004	8.38
2005	8.57
2006	8.75
2007	8.93
2008	9.12
2009	9.3
2010	9.47
2011	9.65
2012	9.83
2013	10
2014	10.18
2015	10.35