Year	Percent
1960	12.5
1961	12.93103
1962	13.11475
1963	7.5188
1964	14.09396
1965	10.34796
1966	10.77616
1967	10.80059
1968	10.2957
1969	9.65872
1970	10.68878
1971	8.43575
1972	11.73444
1973	11.01617
1974	9.7534
1975	8.27565
1976	13.72648
1977	17.59561
1978	11.70769
1979	14.16264
1980	8.80938
1981	9.14335
1982	10.21197
1983	9.04558
1984	11.50401
1985	11.02662
1986	11.72323
1987	9.7449
1988	12.59077
1989	9.74574
1990	7.87299
1991	9.91738
1992	8.74918
1993	9.38196
1994	10.27177
1995	12.92634
1996	5.82032
1997	9.83547
1998	7.99975
1999	7.57576
2000	6.31897
2001	5.1792
2002	4.6858
2003	6.38141
2004	6.95275
2005	8.2025
2006	7.28205
2007	7.25847
2008	9.49176
2009	6.80236
2010	8.91664
2011	9.35371
2012	8.95013
2013	7.39582
2014	7.76818
2015	6.25262
2016	6.24095