Year	Percent
1971	10.96178
1972	12.85648
1973	15.33678
1974	14.34555
1975	16.95285
1976	18.48747
1978	19.21947
1981	18.18678
1982	17.73462
1983	15.5027
1986	26.50343
1987	19.34738
1988	20.37825
1989	18.96913
1990	18.71274
1991	19.32039
1992	15.2119
2004	17.28221
2005	19.25638
2006	20.02763
2008	25.94323
2009	28.51197
2010	29.10172
2011	31.77326
2012	33.95552
2016	33.52613