Year	Percent
1960	35.95095
1961	34.35509
1962	33.43123
1963	33.03365
1964	32.97667
1965	30.62077
1966	31.50081
1967	30.89867
1968	32.76304
1969	32.41889
1970	33.74492
1971	32.53391
1972	38.73632
1973	37.77647
1974	53.59157
1975	46.71254
1976	49.43784
1977	59.80188
1978	46.46882
1979	45.43226
1980	43.64479
1981	49.61012
1982	49.52282
1983	59.2243
1984	59.69243
1985	46.85707
1986	37.85329
1987	32.33673
1988	33.51953
1989	38.95735
1990	34.6357
1991	33.3616
1992	28.42685
1993	31.59103
1994	46.76059
1995	49.29573
1996	47.85
1997	47.94003
1998	48.16768
1999	50.36892
2000	52.11979
2001	56.03163
2002	56.71312
2003	53.18465
2004	54.13954
2005	58.29559
2006	56.25735
2007	58.00134
2008	64.72259
2009	52.51896
2010	53.62127
2011	58.72249
2012	63.02766
2013	62.03714
2014	60.45888
2015	60.16587
2016	55.2869
2017	58.75722