Year	Percent
1960	25.80731
1961	25.54207
1962	25.27124
1963	25.01687
1964	24.80528
1965	24.64893
1966	24.55222
1967	24.50733
1968	24.50846
1969	24.54405
1970	24.60023
1971	24.67299
1972	24.77378
1973	24.89535
1974	25.03446
1975	25.18594
1976	25.34833
1977	25.51779
1978	25.69418
1979	25.72956
1980	25.59509
1981	25.46087
1982	25.3274
1983	25.19202
1984	25.05261
1985	24.90715
1986	24.7574
1987	24.6057
1988	24.45625
1989	24.23362
1990	24.21361
1991	23.92825
1992	23.65519
1993	23.38407
1994	23.15489
1995	22.97388
1996	22.82676
1997	22.69059
1998	22.55885
1999	22.47266
2000	22.4384
2001	22.41425
2002	22.39675
2003	22.37669
2004	22.33052
2005	22.25136
2006	22.20823
2007	22.2107
2008	22.19483
2009	22.38165
2010	22.7719
2011	22.94399
2012	22.91006
2013	22.88352
2014	22.86773
2015	22.86498
2016	22.87937
2017	22.90481