Year	Percent
1960	20.21071
1961	20.80801
1962	19.9663
1963	18.44708
1964	18.51272
1965	15.67066
1966	15.56313
1967	15.42376
1968	18.10876
1969	17.46511
1970	17.41795
1971	13.83975
1972	13.74989
1973	13.32571
1974	14.11431
1975	10.56262
1976	11.72908
1977	15.47478
1978	20.18289
1979	27.00502
1980	25.52052
1981	18.5618
1982	18.81848
1983	21.73522
1984	21.81651
1985	26.14506
1986	16.44261
1987	12.66542
1988	15.09949
1989	11.32964
1990	15.69719
1991	12.08602
1992	12.45363
1993	12.33522
1994	12.77148
1995	12.59989
1996	13.31652
1997	14.47726
1998	13.7029
1999	15.39689
2000	16.76837
2001	16.60138
2002	17.27481
2003	19.01467
2004	22.91223
2005	26.84876
2006	30.53664
2007	31.52212
2008	29.72763
2009	26.44205
2010	27.82616
2011	30.50276
2012	27.44961
2013	24.8031
2014	22.57422
2015	21.27374
2016	22.43821
2017	24.26354