Year	Percent
1960	13.34135
1961	13.62796
1962	12.46394
1963	13.89026
1964	16.43706
1965	16.67063
1966	16.93588
1967	18.63552
1968	22.22751
1969	23.56096
1970	24.59451
1971	21.39235
1972	21.11244
1973	27.71337
1974	35.29244
1975	25.93832
1976	27.67565
1977	26.77413
1978	22.59514
1979	24.1747
1980	24.52752
1981	23.26602
1982	29.06435
1983	28.31678
1984	23.65486
1985	19.04991
1986	21.32401
1987	19.63048
1988	18.76744
1989	22.49821
1990	22.77698
1991	21.47935
1992	20.04576
1993	19.08077
1994	21.66331
1995	22.55142
1996	22.58187
1997	21.1106
1998	19.69868
1999	16.8809
2000	18.27475
2001	19.97215
2002	21.63446
2003	25.60073
2004	31.13839
2005	35.54814
2006	41.77171
2007	41.79566
2008	44.90656
2009	35.72263
2010	41.18746
2011	44.0917
2012	47.1662
2013	44.09248
2014	43.29309
2015	30.8683
2016	24.48801
2017	24.90414