Year	Percent
1960	0.69802
1961	37.80577
1962	37.68096
1963	36.68452
1964	47.12121
1965	50.70676
1966	45.59769
1967	46.98924
1968	49.78297
1969	52.20498
1970	58.04408
1971	49.10529
1972	51.39721
1973	53.55143
1974	56.17922
1975	64.17706
1976	55.53681
1977	53.91528
1978	55.15556
1979	59.70041
1980	59.30568
1981	51.871
1982	46.01289
1983	44.14698
1984	48.42679
1985	47.20034
1986	42.91792
1987	48.3478
1988	50.29262
1989	48.42111
1990	52.74431
1991	53.187
1992	62.8502
1993	41.82288
1994	70.99324
1995	62.97148
1996	48.44294
1997	49.48869
1998	54.0391
1999	63.4037
2000	52.25102
2001	58.95708
2002	31.52924
2003	40.85976
2004	40.72763
2005	45.78847
2006	46.903
2007	50.68381
2008	57.93517
2009	51.84289
2010	46.54286
2011	48.14245
2012	58.76785
2013	73.43145
2014	67.98408
2015	53.21839
2016	63.36334
2017	54.88841