Year	Years
1970	2.98
1971	3.08
1972	3.19
1973	3.3
1974	3.41
1975	3.53
1976	3.65
1977	3.77
1978	3.9
1979	4.03
1980	4.17
1981	4.31
1982	4.45
1983	4.6
1984	4.75
1985	4.91
1986	5.07
1987	5.24
1988	5.41
1989	5.58
1990	5.76
1991	5.94
1992	6.12
1993	6.3
1994	6.49
1995	6.68
1996	6.86
1997	7.05
1998	7.24
1999	7.42
2000	7.61
2001	7.79
2002	7.98
2003	8.16
2004	8.35
2005	8.53
2006	8.71
2007	8.89
2008	9.06
2009	9.24
2010	9.41
2011	9.59
2012	9.76
2013	9.93
2014	10.09
2015	10.26