Year	Percent
1960	25.76923
1961	23.74731
1962	25.18688
1963	23.92522
1964	25.48906
1965	13.80663
1966	13.53249
1967	15.81534
1968	18.65671
1969	13.97097
1970	16.20085
1971	19.57723
1972	20.24176
1973	23.87817
1974	27.30155
1975	25.36216
1976	24.37141
1977	23.8048
1978	25.68756
1979	26.1295
1980	26.47427
1981	21.53524
1982	22.55912
1983	22.35828
1984	25.04654
1985	27.24342
1986	26.00211
1987	29.97397
1988	29.92671
1989	30.30057
1990	30.02111
1991	30.90908
1992	30.05377
1993	28.85623
1994	32.76722
1995	34.62137
1996	37.58885
1997	36.28287
1998	34.94759
1999	38.01423
2000	47.18524
2001	41.03673
2002	40.18712
2003	39.85289
2004	43.66883
2005	49.11667
2006	53.07802
2007	55.31404
2008	60.99198
2009	46.31012
2010	54.74886
2011	58.98326
2012	56.00453
2013	54.65589
2014	52.54363
2015	40.13337
2016	33.5874
2017	37.97151