Year	Percent
1960	47.20864
1961	46.5355
1962	47.82126
1963	46.95749
1964	48.64626
1965	49.88259
1966	50.99902
1967	49.92905
1968	46.91493
1969	47.40122
1970	47.05094
1971	47.40362
1972	48.70142
1973	46.60169
1974	41.1295
1975	42.663
1976	43.30194
1977	40.07868
1978	41.67992
1979	44.2379
1980	42.2571
1981	43.78545
1982	46.88315
1983	44.98411
1984	44.64659
1985	45.39489
1986	45.58953
1987	44.91685
1988	46.28428
1989	46.94301
1990	46.9874
1991	47.01642
1992	47.9881
1993	49.26975
1994	49.62199
1995	50.1759
1996	50.88671
1997	51.05774
1998	51.21879
1999	51.91019
2000	52.7546
2001	53.11279
2002	57.71006
2003	58.34489
2004	58.83809
2005	57.99243
2006	58.02142
2007	58.39702
2008	57.2496
2009	57.63659
2010	54.63836
2011	55.13839
2012	55.63484
2013	56.36441
2014	56.90119
2015	57.3792
2016	56.8641
2017	55.7737