Year	Percent
1960	10.28796
1961	10.90164
1962	9.2908
1963	9.87634
1964	9.69088
1965	9.135
1966	9.03061
1967	9.44984
1968	9.01347
1969	8.97995
1970	9.20592
1971	8.68909
1972	7.99806
1973	9.67583
1974	13.8658
1975	12.32932
1976	12.32944
1977	11.07479
1978	9.06721
1979	12.05443
1980	14.10068
1981	13.5078
1982	13.37251
1983	11.7628
1984	11.94736
1985	10.70285
1986	7.23875
1987	7.16896
1988	7.61089
1989	8.76042
1990	9.44299
1991	8.28787
1992	7.63772
1993	6.93602
1994	7.10082
1995	7.70769
1996	9.04543
1997	9.49189
1998	8.70754
1999	8.3972
2000	9.19517
2001	9.56903
2002	9.66739
2003	9.94384
2004	10.95032
2005	12.50305
2006	14.45888
2007	15.60057
2008	16.97498
2009	11.96999
2010	13.57625
2011	15.46801
2012	16.09137
2013	18.23212
2014	20.00547
2015	18.00747
2016	15.14743