Year	Years
1970	2.22
1971	2.3
1972	2.37
1973	2.44
1974	2.52
1975	2.6
1976	2.68
1977	2.76
1978	2.85
1979	2.93
1980	3.02
1981	3.11
1982	3.21
1983	3.3
1984	3.4
1985	3.5
1986	3.6
1987	3.7
1988	3.8
1989	3.91
1990	4.02
1991	4.12
1992	4.23
1993	4.34
1994	4.45
1995	4.57
1996	4.68
1997	4.79
1998	4.9
1999	5.01
2000	5.13
2001	5.25
2002	5.36
2003	5.48
2004	5.6
2005	5.73
2006	5.85
2007	5.98
2008	6.1
2009	6.23
2010	6.37
2011	6.5
2012	6.64
2013	6.77
2014	6.92
2015	7.06