Year	Percent
1960	56.55612
1961	51.04866
1962	50.79572
1963	54.51964
1964	61.74547
1965	42.32596
1966	43.24766
1967	38.31156
1968	38.92837
1969	37.73618
1970	31.66189
1971	29.4331
1972	27.66287
1973	29.20523
1974	34.87768
1975	34.96156
1976	32.14052
1977	35.61539
1978	66.28936
1979	72.2876
1980	77.12526
1981	66.64637
1982	59.99457
1983	55.84459
1984	54.90219
1985	52.45497
1986	47.96095
1987	51.27079
1988	53.6085
1989	53.42575
1990	57.26699
1991	56.01997
1992	61.3727
1993	66.39146
1994	68.05999
1995	69.87115
1996	68.62268
1997	69.59356
1998	67.83171
1999	67.41683
2000	77.19762
2001	68.50266
2002	65.33327
2003	62.47874
2004	66.44773
2005	62.20024
2006	60.64839
2007	58.85593
2008	55.02829
2009	41.34784
2010	38.98181
2011	46.72238
2012	41.74689
2013	37.97227
2014	38.70346
2015	36.59757
2016	36.05953
2017	36.92471