Year	Percent
1960	29.72406
1961	28.31203
1962	26.71762
1963	24.16799
1964	26.92313
1965	26.5121
1966	28.01889
1967	29.27592
1968	34.876
1969	35.15664
1970	31.53938
1971	32.08827
1972	27.33653
1973	31.50183
1974	24.32382
1975	25.76911
1976	18.21317
1977	12.22625
1978	15.04522
1979	19.21864
1980	15.90581
1981	20.2981
1982	20.86891
1983	22.25877
1984	23.12229
1985	24.30381
1986	16.94417
1987	20.64907
1988	23.62214
1989	26.61117
1990	25.88439
1991	24.36428
1992	29.82856
1993	25.2612
1994	24.23186
1995	25.25957
1996	25.554
1997	25.69477
1998	22.60035
1999	21.26335
2000	23.46334
2001	25.88036
2002	27.33772
2003	26.24745
2004	26.46721
2005	26.94238
2006	28.42251
2007	26.57131
2008	24.35054
2009	21.05638
2010	20.20819
2011	21.44363
2012	19.94225
2013	21.27699
2014	22.47614
2015	21.26985
2016	21.34716
2017	21.78552