Year	Percent
1960	36.76079
1961	35.61992
1962	35.74879
1963	36.81818
1964	58.37815
1965	49.26073
1966	29.19345
1967	28.04233
1968	23.45875
1969	22.16749
1970	21.34331
1971	20.41382
1972	24.04381
1973	33.60629
1974	43.70591
1975	39.46237
1976	51.33531
1977	37.36349
1978	32.42692
1979	22.86079
1980	26.41842
1981	31.21309
1982	27.70038
1983	15.60661
1984	11.79193
1985	14.44031
1986	21.95286
1987	25.96826
1988	16.68102
1989	20.8361
1990	10.7726
1991	11.36962
1992	11.13363
1993	9.93347
1994	13.68961
1995	15.2576
1996	15.58124
1997	17.64325
1998	25.49146
1999	17.64979
2000	12.35886
2001	28.90113
2002	22.03324
2003	22.83347
2004	22.44866
2005	24.85453
2006	18.39872
2007	42.30244
2008	45.46298
2009	47.08592
2010	37.53856
2011	53.18736
2012	57.84572
2013	62.86754
2014	70.66011
2015	67.44289
2016	65.96352
2017	56.51615