Year	Percent
1960	12.61155
1961	8.86714
1962	11.9039
1963	16.01828
1964	18.32098
1965	9.77367
1966	15.85527
1967	15.52957
1968	15.37392
1969	18.13084
1970	19.13962
1971	17.85286
1972	19.70513
1973	22.09664
1974	23.34906
1975	24.51032
1976	22.54138
1977	21.78936
1978	23.67208
1979	25.35462
1980	25.12442
1981	23.6136
1982	19.96484
1983	21.0624
1984	21.32928
1985	17.59607
1986	19.77594
1987	24.22914
1988	24.55061
1989	28.47569
1990	25.14078
1991	16.64807
1992	18.79127
1993	19.75814
1994	21.0044
1995	20.04954
1996	20.05427
1997	22.10141
1998	28.06938
1999	27.11277
2000	27.89266
2001	26.77064
2002	26.95676
2003	19.40916
2004	20.62735
2005	24.77307
2006	26.92687
2007	28.35139
2008	30.02372
2009	23.57348
2010	26.37997
2011	25.02626
2012	24.29574
2013	22.72367
2014	23.02531
2015	22.57696
2016	21.94404
2017	21.83129