Year	Percent
1960	16.62452
1961	19.50334
1962	18.38353
1963	19.92631
1964	19.92784
1965	20
1966	23.19807
1967	21.50406
1968	22.79018
1969	23.11155
1970	21.58563
1971	21.02565
1972	18.32323
1973	18.87873
1974	20.20715
1975	20.89014
1976	17.5247
1977	20.04897
1978	24.0574
1979	30.38713
1980	29.73786
1981	22.81624
1982	20.66599
1983	17.53414
1984	17.90882
1985	20.50792
1986	15.5469
1987	22.50598
1988	23.09889
1989	22.27096
1990	28.02719
1991	26.68871
1992	24.66727
1993	24.61533
1994	29.59885
1995	31.71146
1996	26.00429
1997	29.95999
1998	29.27742
1999	32.20959
2000	38.00511
2001	32.29217
2002	22.57385
2003	32.07349
2004	47.48389
2005	45.55279
2006	45.7686
2007	52.06714
2008	56.90847
2009	51.62729
2010	43.04859
2011	42.33366
2012	39.06393
2013	38.75168
2014	37.13865
2015	35.53078
2016	35.75932
2017	39.03527