Year	Years
1970	2.18
1971	2.24
1972	2.29
1973	2.35
1974	2.41
1975	2.47
1976	2.53
1977	2.59
1978	2.66
1979	2.72
1980	2.79
1981	2.86
1982	2.92
1983	2.99
1984	3.07
1985	3.14
1986	3.21
1987	3.29
1988	3.37
1989	3.45
1990	3.53
1991	3.61
1992	3.69
1993	3.78
1994	3.87
1995	3.95
1996	4.04
1997	4.14
1998	4.23
1999	4.33
2000	4.42
2001	4.52
2002	4.62
2003	4.72
2004	4.82
2005	4.93
2006	5.03
2007	5.14
2008	5.25
2009	5.36
2010	5.47
2011	5.58
2012	5.7
2013	5.81
2014	5.93
2015	6.05