Year	Percent
1966	36.17061
1967	40.52147
1968	39.99044
1969	40.39288
1970	37.79156
1971	32.36725
1972	33.77306
1973	35.10266
1974	38.97303
1975	44.70857
1976	41.05685
1977	36.7355
1978	33.68122
1979	34.95956
1980	42.73621
1981	43.96109
1982	44.33439
1983	50.48829
1984	51.12494
1985	43.86485
1986	46.62415
1987	49.41809
1988	50.36572
1989	55.05998
1990	59.90274
1991	29.43892
1992	30.59271
1993	28.19202
1994	21.23962
1995	23.77565
1996	21.79867
1997	22.9322
1998	25.30557
1999	24.39736
2000	25.79867
2001	21.8208
2002	27.15738
2003	31.09379
2004	34.22703
2005	32.7708
2006	33.84825
2007	28.88632
2008	23.40783
2009	25.35317
2010	23.78291
2011	26.45759
2012	30.85197
2013	29.3528
2014	29.24024
2015	24.69869
2016	22.96223
2017	20.81245