Year	Percent
1960	10.51775
1961	9.54492
1962	13.46999
1964	8.64297
1965	8.87795
1966	7.74718
1967	8.21396
1968	12.16488
1969	10.82617
1970	11.22059
1971	8.43629
1972	10.77156
1973	15.06947
1974	12.66015
1975	15.94892
1976	14.72599
1977	14.50413
1978	14.70561
1979	15.92857
1980	17.24985
1981	14.54612
1982	15.5594
1983	14.63891
1984	17.68602
1985	16.55512
1986	14.44968
1987	11.21821
1988	7.85393
1989	7.97254
1990	6.86809
1991	10.42579
1992	8.99066
1993	7.2381
1994	7.36414
1995	6.94969
1996	6.04192
1997	5.88276
1998	5.80838
1999	5.81058
2000	5.45366
2001	5.48055
2002	5.4125
2003	6.24832
2004	5.54184
2005	5.02642
2006	4.39445
2007	4.10054
2008	3.55234
2009	4.02771
2010	4.05614