Year	Percent
1960	27.92747
1961	24.92263
1962	22.45082
1963	22.21953
1964	19.09752
1965	18.08364
1966	19.35016
1967	20.65943
1968	21.11722
1969	19.839
1970	21.69438
1971	15.48059
1972	19.44215
1973	15.29477
1974	21.24243
1975	26.5756
1976	30.91383
1977	32.5047
1978	29.39459
1979	27.77299
1980	26.95065
1981	25.85005
1982	23.23833
1983	35.92511
1984	35.27659
1985	34.17147
1986	33.29868
1987	31.63898
1988	31.19249
1989	33.17948
1990	32.64923
1991	28.93043
1992	29.10354
1993	26.46288
1994	26.89049
1995	25.76996
1996	27.8814
1997	26.92144
1998	25.92775
1999	23.32394
2000	25.2418
2001	24.50381
2002	28.11158
2003	36.49456
2004	44.16816
2005	42.04891
2006	44.92146
2007	43.33604
2008	49.43408
2009	38.88546
2010	38.09388
2011	38.85984
2012	39.71826
2013	35.99637
2014	36.02039
2015	32.2236
2016	28.72245
2017	29.10994