Year	Years
1970	2
1971	2.05
1972	2.1
1973	2.16
1974	2.22
1975	2.28
1976	2.34
1977	2.4
1978	2.46
1979	2.53
1980	2.59
1981	2.66
1982	2.73
1983	2.81
1984	2.88
1985	2.96
1986	3.04
1987	3.12
1988	3.2
1989	3.28
1990	3.37
1991	3.46
1992	3.55
1993	3.64
1994	3.74
1995	3.84
1996	3.94
1997	4.04
1998	4.14
1999	4.24
2000	4.34
2001	4.45
2002	4.55
2003	4.66
2004	4.77
2005	4.87
2006	4.98
2007	5.09
2008	5.21
2009	5.32
2010	5.43
2011	5.55
2012	5.66
2013	5.78
2014	5.9
2015	6.02