Year	Years
1970	1.98
1971	2.03
1972	2.08
1973	2.13
1974	2.19
1975	2.24
1976	2.3
1977	2.36
1978	2.41
1979	2.48
1980	2.54
1981	2.6
1982	2.66
1983	2.73
1984	2.8
1985	2.86
1986	2.93
1987	3
1988	3.08
1989	3.15
1990	3.23
1991	3.3
1992	3.38
1993	3.46
1994	3.54
1995	3.62
1996	3.71
1997	3.79
1998	3.88
1999	3.97
2000	4.06
2001	4.15
2002	4.24
2003	4.33
2004	4.43
2005	4.53
2006	4.63
2007	4.73
2008	4.83
2009	4.93
2010	5.04
2011	5.14
2012	5.25
2013	5.36
2014	5.47
2015	5.59