Year	Percent
1960	1.9759
1961	2.02877
1962	2.07594
1963	2.11052
1964	2.1295
1965	2.13965
1966	2.15145
1967	2.17174
1968	2.19974
1969	2.23762
1970	2.28499
1971	2.31975
1972	2.35854
1973	2.4381
1974	2.56719
1975	2.71916
1976	2.88147
1977	3.00467
1978	3.04434
1979	2.9824
1980	2.8575
1981	2.71506
1982	2.60268
1983	2.53541
1984	2.52929
1985	2.56273
1986	2.6032
1987	2.62564
1988	2.63093
1989	2.61241
1990	2.57904
1991	2.54561
1992	2.52124
1993	2.50297
1994	2.493
1995	2.48943
1996	2.48837
1997	2.48818
1998	2.49072
1999	2.49581
2000	2.5034
2001	2.51121
2002	2.52111
2003	2.53684
2004	2.55924
2005	2.58522
2006	2.61039
2007	2.63165
2008	2.64897
2009	2.66122
2010	2.66875
2011	2.67475
2012	2.67766
2013	2.67292
2014	2.65955
2015	2.64036
2016	2.61903
2017	2.5987