Year	Percent
1960	19.15793
1961	23.42766
1962	31.70181
1963	34.91629
1964	37.91902
1965	28.68526
1966	26.59381
1967	23.40824
1968	19.64912
1969	16.33466
1970	23.11223
1971	19.89078
1972	21.38005
1973	20.14383
1974	23.84722
1975	18.5758
1976	22.19409
1977	26.9289
1978	47.90682
1979	42.69242
1980	40.65291
1981	31.04412
1982	30.18845
1983	32.77841
1984	28.70459
1985	26.21807
1986	19.95518
1987	14.85748
1988	23.54923
1989	23.93041
1990	15.11405
1991	15.6494
1992	19.71806
1993	18.05659
1994	17.35446
1995	16.02303
1996	17.03251
1997	17.21751
1998	19.10388
1999	16.67689
2000	23.54548
2001	23.69791
2002	21.41656
2003	19.29385
2004	19.37617
2005	17.35583
2006	16.47765
2007	16.043
2008	15.7015
2009	15.38431
2010	14.48509
2011	12.89877
2012	12.25478
2013	12.10604
2014	12.31601
2015	11.44135
2016	12.43931