Year	Percent
1960	52.10729
1961	52.13715
1962	51.01374
1963	56.25869
1964	58.21461
1965	41.49032
1966	41.40519
1967	39.09659
1968	36.67676
1969	34.86402
1970	36.03387
1971	35.94439
1972	29.83226
1973	26.64202
1974	25.15501
1975	19.6712
1976	21.9097
1977	28.24683
1978	24.86344
1979	29.54178
1980	51.26104
1981	43.96919
1982	33.34099
1983	33.43252
1984	20.54957
1985	20.28601
1986	18.93847
1987	18.61389
1988	17.79094
1989	10.32885
1990	10.2221
1991	11.9215
1992	22.6425
1993	22.17089
1994	32.17698
1995	26.33856
1996	29.41476
1997	29.84368
1998	29.11243
1999	31.0241
2000	31.30545
2001	35.006
2002	24.60734
2003	30.08823
2004	29.96767
2005	31.80608
2006	35.39819
2007	39.29143
2008	43.89453
2009	32.00515
2010	31.12447
2011	38.60994
2012	36.34825
2013	33.43657
2014	30.54202
2015	28.76149
2016	30.36585
2017	31.78306