Year	Years
1970	2.45
1971	2.55
1972	2.64
1973	2.74
1974	2.85
1975	2.96
1976	3.07
1977	3.19
1978	3.32
1979	3.45
1980	3.58
1981	3.72
1982	3.87
1983	4.03
1984	4.19
1985	4.35
1986	4.53
1987	4.71
1988	4.9
1989	5.1
1990	5.3
1991	5.51
1992	5.73
1993	5.95
1994	6.18
1995	6.41
1996	6.61
1997	6.8
1998	7
1999	7.19
2000	7.38
2001	7.57
2002	7.77
2003	7.96
2004	8.14
2005	8.33
2006	8.52
2007	8.71
2008	8.89
2009	9.07
2010	9.26
2011	9.44
2012	9.62
2013	9.8
2014	9.97
2015	10.15