Year	Percent
1960	39.98162
1961	37.78377
1962	36.38326
1963	33.08454
1964	40.8481
1965	40.81403
1966	36.85209
1967	43.66711
1968	39.17981
1969	40.7143
1970	39.21026
1971	35.74061
1972	35.34929
1973	31.38838
1974	52.78875
1975	47.27839
1976	46.87327
1977	48.47914
1978	45.13546
1979	44.89777
1980	46.32784
1981	45.22661
1982	38.57634
1983	25.91792
1984	42.37867
1985	38.91207
1986	29.19352
1987	44.62794
1988	39.31307
1989	50.12603
1990	52.80257
1991	50.82608
1992	48.33183
1993	46.78947
1994	44.71171
1995	41.52642
1996	48.25396
1997	44.82225
1998	36.70597
1999	35.75027
2000	42.46346
2001	36.60582
2002	42.78444
2003	43.63277
2004	50.10725
2005	54.80262
2006	54.0633
2007	50.38834
2008	46.04192
2009	30.06268
2010	26.63963
2011	44.49255
2012	38.99197
2013	37.06847
2014	24.43884