Year	Years
1970	2.62
1971	2.69
1972	2.76
1973	2.83
1974	2.9
1975	2.97
1976	3.04
1977	3.12
1978	3.19
1979	3.27
1980	3.34
1981	3.42
1982	3.49
1983	3.56
1984	3.64
1985	3.71
1986	3.78
1987	3.85
1988	3.92
1989	3.99
1990	4.05
1991	4.12
1992	4.18
1993	4.23
1994	4.29
1995	4.34
1996	4.43
1997	4.53
1998	4.62
1999	4.73
2000	4.83
2001	4.94
2002	5.05
2003	5.17
2004	5.29
2005	5.41
2006	5.53
2007	5.66
2008	5.79
2009	5.92
2010	6.05
2011	6.19
2012	6.33
2013	6.47
2014	6.61
2015	6.76