Year	Percent
1960	47.70378
1961	45.14401
1962	43.48192
1963	43.8324
1964	45.88486
1965	45.08242
1966	41.57477
1967	42.03417
1968	40.23955
1969	39.01129
1970	39.02328
1971	38.588
1972	37.71799
1973	38.32645
1974	44.94937
1975	44.8162
1976	41.34978
1977	39.78829
1978	43.61895
1979	47.26432
1980	54.37549
1981	48.62573
1982	43.6292
1983	38.65562
1984	37.68528
1985	39.89686
1986	38.21434
1987	33.97664
1988	34.30532
1989	31.56568
1990	36.30187
1991	33.97356
1992	32.09181
1993	32.91868
1994	34.82658
1995	37.56522
1996	40.24376
1997	41.9599
1998	40.35874
1999	39.08529
2000	43.76444
2001	47.2908
2002	50.96412
2003	43.49592
2004	43.51038
2005	44.21523
2006	50.36207
2007	52.91504
2008	63.53959
2009	45.66712
2010	50.1422
2011	55.95032
2012	57.21459
2013	60.6504
2014	61.02304
2015	58.56364
2016	56.39624
2017	54.48477