Year	Percent
1960	38.97554
1961	39.04361
1962	36.93074
1963	46.41538
1964	46.93022
1965	51.12237
1966	52.00771
1967	46.97866
1968	44.91022
1969	43.33303
1970	46.60708
1971	49.14666
1972	42.4462
1973	43.76777
1974	54.76995
1975	47.59475
1976	50.62529
1977	55.07925
1978	51.53236
1979	43.73386
1980	46.38477
1981	44.89027
1982	41.43617
1983	36.96148
1984	41.18591
1985	39.02179
1986	38.85828
1987	34.07428
1988	36.45555
1989	37.64284
1990	37.95921
1991	37.33065
1992	38.73736
1993	54.73079
1994	51.45391
1995	53.82295
1996	41.64087
1997	40.65334
1998	36.93061
1999	35.5071
2000	38.0863
2001	39.55026
2002	40.77574
2003	41.17221
2004	44.96166
2005	49.45095
2006	41.56587
2007	40.89737
2008	44.93299
2009	39.6133
2010	43.155
2011	48.95249
2012	44.53569
2013	40.31791
2014	39.88939
2015	34.3702
2016	27.93939
2017	29.93729