Year	Percent
1960	16.85217
1961	16.49321
1962	17.88972
1963	16.24608
1964	15.65425
1965	8.97966
1966	10.4857
1967	10.10719
1968	11.04217
1969	8.50295
1970	9.44123
1971	10.58041
1972	12.40791
1973	17.87804
1974	22.65205
1975	16.07089
1976	16.03564
1977	16.30288
1978	14.73198
1979	17.90808
1980	17.14803
1981	14.61785
1982	14.65649
1983	15.55961
1984	17.37642
1985	19.68137
1986	15.6294
1987	15.36609
1988	19.00585
1989	20.28305
1990	22.76437
1991	23.67458
1992	24.13374
1993	20.03584
1994	20.27982
1995	21.2869
1996	22.27328
1997	21.53493
1998	17.89195
1999	26.37754
2000	32.12754
2001	23.22275
2002	21.49237
2003	22.5984
2004	24.55435
2005	27.61817
2006	30.33307
2007	31.93177
2008	34.16364
2009	25.24911
2010	27.89496
2011	31.1212
2012	30.16481
2013	28.63829
2014	28.05185
2015	21.25822
2016	19.67991
2017	20.75524