Year	Percent
1960	59.37167
1961	61.49745
1962	62.30312
1963	61.27341
1964	61.0881
1965	61.93416
1966	61.07011
1967	60.27397
1968	61.09325
1969	62.84468
1970	58.15789
1971	60.99212
1972	62.31884
1973	62.16887
1974	59.4748
1975	53.10219
1976	48.91847
1977	52.92553
1978	54.46293
1979	49.29411
1980	41.70366
1981	41.22208
1982	39.57746
1983	38.08809
1984	36.49453
1985	38.63827
1986	55.26431
1987	52.27446
1988	56.21684
1989	49.08645
1990	46.49606
1991	52.64733
1992	52.96239
1993	53.45349
1994	44.20172
1995	44.67904
1996	39.17058
1997	33.9972
1998	42.98757
1999	30.37328
2000	22.54308
2001	28.71161
2002	30.4195
2003	32.55242
2004	28.62611
2005	23.5743
2006	20.53876
2007	22.43186
2008	18.90938
2009	24.37716
2010	20.7924
2011	19.99124
2012	21.30654
2013	23.62193
2014	25.74869
2015	38.08213
2016	41.06584
2017	38.49245