Year	Years
1970	1.98
1971	2.05
1972	2.11
1973	2.17
1974	2.24
1975	2.3
1976	2.37
1977	2.44
1978	2.52
1979	2.59
1980	2.67
1981	2.74
1982	2.82
1983	2.9
1984	2.99
1985	3.07
1986	3.16
1987	3.25
1988	3.34
1989	3.43
1990	3.52
1991	3.62
1992	3.72
1993	3.82
1994	3.92
1995	4.03
1996	4.14
1997	4.26
1998	4.38
1999	4.5
2000	4.62
2001	4.74
2002	4.87
2003	5
2004	5.13
2005	5.26
2006	5.4
2007	5.53
2008	5.67
2009	5.81
2010	5.95
2011	6.1
2012	6.24
2013	6.39
2014	6.53
2015	6.68