Year	Percent
1981	34.02084
1982	29.73934
1983	21.87475
1984	12.42067
1985	11.35743
1986	15.7025
1987	12.66393
1988	9.84832
1989	11.7467
1990	14.42773
1991	13.79346
1992	12.80218
1993	13.61295
1994	11.19636
1995	7.08323
1996	7.30372
1997	8.37214
1998	8.61986
1999	7.01157
2000	7.03106
2001	7.5938
2002	7.02033
2003	9.91352
2004	7.40132
2005	5.46702
2006	8.27372
2007	9.25642
2008	8.32982
2009	12.09461
2010	17.29074
2011	16.21198
2012	14.90769
2013	14.90391
2014	15.8027
2015	15.4901
2016	15.34003