Year	Percent
1960	16.72493
1961	19.84098
1962	13.88957
1963	17.78283
1964	21.84455
1965	21.87223
1966	21.82035
1967	19.78228
1968	17.81211
1969	19.52529
1970	22.49565
1971	21.8019
1972	20.87535
1973	23.18011
1974	22.01624
1975	22.44458
1976	22.98923
1977	27.33238
1978	29.76217
1979	27.96545
1980	26.53612
1981	25.94047
1982	23.18829
1983	18.41277
1984	11.65078
1985	12.95138
1986	12.06341
1987	12.31724
1988	12.65035
1989	8.90396
1990	6.6888
1991	7.358
1992	6.92388
1993	9.79307
1994	13.71572
1995	15.59845
1996	12.11207
1997	14.42445
1998	13.51927
1999	13.3079
2000	10.48456
2001	10.51608
2002	9.36477
2003	9.07918
2004	10.10124
2005	13.93882
2006	10.59141
2007	12.67023
2008	12.06918
2009	8.69686
2010	13.43703
2011	4.70372
2012	15.11865
2013	20.71073
2014	19.7932
2015	20.10382
2016	20.72176
2017	22.63613