Year	Years
1970	2.23
1971	2.3
1972	2.36
1973	2.43
1974	2.5
1975	2.58
1976	2.65
1977	2.73
1978	2.81
1979	2.9
1980	2.98
1981	3.07
1982	3.17
1983	3.26
1984	3.36
1985	3.47
1986	3.57
1987	3.69
1988	3.8
1989	3.92
1990	4.04
1991	4.17
1992	4.3
1993	4.43
1994	4.57
1995	4.7
1996	4.82
1997	4.94
1998	5.06
1999	5.18
2000	5.3
2001	5.42
2002	5.54
2003	5.66
2004	5.78
2005	5.91
2006	6.03
2007	6.16
2008	6.28
2009	6.41
2010	6.54
2011	6.67
2012	6.79
2013	6.92
2014	7.05
2015	7.18