Year	Percent
1980	23.79342
1981	22.9518
1982	18.16138
1983	17.0035
1984	13.13313
1985	9.86953
1986	8.10147
1987	12.76766
1988	14.95097
1989	14.75392
1990	26.91826
1991	15.34032
1992	18.35043
1993	15.44436
1994	19.22418
1995	19.52477
1996	20.70365
1997	17.94555
1998	22.62171
1999	20.77704
2000	17.1007
2001	22.31873
2002	18.52172
2003	19.36925
2004	19.06721
2005	19.69108
2006	22.26201
2007	24.36401
2008	27.83279
2009	26.45273
2010	24.1243
2011	22.37655
2012	26.7236
2013	25.06738
2014	33.60325
2015	33.83769
2016	23.72379
2017	17.64696