Year	Percent
1960	39.64394
1961	42.5255
1962	44.83899
1963	47.34536
1964	48.5767
1965	50.60976
1966	50.94851
1967	50.77349
1968	62.94737
1969	52.56526
1970	60.91371
1971	61.56388
1972	60.54288
1973	61.96518
1974	64.77519
1975	63.79212
1976	66.32148
1977	69.30966
1978	68.52439
1979	65.24993
1980	66.4423
1981	71.53033
1982	69.2742
1983	62.56562
1984	57.9622
1985	51.23176
1986	49.12874
1987	48.44219
1988	43.92965
1989	46.13627
1990	49.79191
1991	46.52887
1992	41.57169
1993	39.11241
1994	40.35821
1995	43.75867
1996	37.12713
1997	47.72368
1998	52.55187
1999	43.73181
2000	40.09292
2001	38.86746
2002	39.67835
2003	37.00718
2004	41.38404
2005	35.5818
2006	34.08012
2007	40.58856
2008	51.04194
2009	51.88507
2010	51.26433
2011	52.46403
2012	60.29247
2013	61.43659
2014	53.94247
2015	53.50739
2016	42.01987