Year	Percent
1960	62.15187
1961	59.41732
1962	58.03792
1963	57.742
1964	58.13479
1965	53.81266
1966	58.84746
1967	52.14077
1968	54.59479
1969	62.40552
1970	54.72333
1971	46.19358
1972	47.57383
1973	53.61753
1974	54.78618
1975	41.66879
1976	40.56795
1977	37.65606
1978	39.36997
1979	41.98993
1980	39.10106
1981	36.85086
1982	35.29608
1983	40.05788
1984	39.23139
1985	42.03397
1986	44.35325
1987	41.12549
1988	44.04308
1989	47.2835
1990	45.29407
1991	46.28369
1992	43.7348
1993	37.44289
1994	37.32495
1995	34.31351
1996	33.202
1997	32.38064
1998	27.27739
1999	22.81984
2000	23.24389
2001	23.36061
2002	23.87555
2003	24.13497
2004	25.69613
2005	26.84962
2006	30.39612
2007	31.90968
2008	30.99062
2009	30.22447
2010	32.23886
2011	34.44343
2012	32.01034
2013	32.60413
2014	32.94433
2015	33.65772
2016	34.87714
2017	35.70742