Year	Percent
1965	23.75939
1966	20.99473
1967	20.62527
1968	22.12355
1969	23.38343
1970	26.20993
1971	23.01816
1972	20.39187
1973	20.69373
1974	25.43809
1975	22.68496
1976	22.6426
1977	25.05995
1978	23.6552
1979	21.07855
1980	27.88475
1981	21.86705
1982	33.21434
1983	30.3976
1984	33.47859
1985	33.44877
1986	23.28137
1987	16.69426
1988	16.03297
1989	20.70704
1990	20.18291
1991	19.99888
1992	20.54702
1993	13.91794
1994	21.0894
1995	20.6371
1996	23.26042
1997	24.88003
1998	22.5484
1999	20.04833
2000	25.90821
2001	25.8394
2002	24.2969
2003	20.92778
2004	22.70946
2005	24.59798
2006	25.63861
2007	28.8854
2008	29.0577
2009	21.40326
2010	22.17214
2011	25.93207
2012	26.1182
2013	25.56776
2014	24.93807
2015	22.25967
2016	18.58348
2017	16.95987