Year	Percent
1960	4.13223
1961	4.45344
1962	4.87805
1963	9.1716
1964	8.88889
1965	11.25828
1966	8.57143
1967	6.77291
1968	8.89968
1969	10.09464
1970	9.784
1971	10.92234
1972	14.76323
1973	12.94872
1974	14.02062
1975	12.67606
1976	13.21739
1977	11.6629
1978	10.84175
2002	32.38672
2003	43.55687
2004	33.99649
2005	27.39526
2006	26.47029
2007	17.82371
2008	17.99297
2009	14.70759
2010	10.02385
2011	6.10727
2012	5.51685
2013	6.3079
2014	6.5677
2015	7.00212
2016	6.89625