Year	Percent
1960	8.74087
1961	7.3683
1962	6.96091
1963	6.86531
1964	6.63308
1965	6.82813
1966	6.72946
1967	6.25347
1968	6.22094
1969	5.45305
1970	4.95239
1971	4.92082
1972	5.75545
1973	8.00008
1974	10.33349
1975	9.5542
1976	8.83691
1977	8.38462
1978	14.10034
1979	16.39814
1980	19.90068
1981	22.47502
1982	20.28673
1983	18.90702
1984	20.60001
1985	22.4894
1986	24.55329
1987	30.27882
1988	32.90629
1989	32.11336
1990	31.98932
1991	35.39657
1992	38.77229
1993	44.00477
1994	41.92994
1995	38.23631
1996	33.56088
1997	33.81454
1998	31.48061
1999	32.96443
2000	39.15452
2001	38.05082
2002	42.21319
2003	51.25545
2004	59.04604
2005	62.20154
2006	63.96638
2007	61.27422
2008	55.74478
2009	43.20069
2010	48.74916
2011	48.09296
2012	45.17374
2013	43.29029
2014	41.03581
2015	35.72664
2016	32.93325
2017	33.54566