Year	Percent
1983	4.8256
1984	5.0251
1985	4.5559
1986	4.1578
1987	4.0263
1988	3.7769
1989	3.3362
1990	3.1596
1991	3.5958
1992	3.7125
1993	4.363
1994	4.7671
1995	5.0895
1996	4.7657
1997	4.9339
1998	5.7286
1999	6.2123
2000	6.1418
2001	5.6139
2002	5.437
2003	5.2039
2004	5.4166
2005	5.4271
2006	5.0107
2007	4.7406
2008	4.525
2009	6.4873
2010	9.4813
2011	14.5687
2012	20.9915
2013	23.6927
2014	22.9638
2015	20.8732
2016	18.4448
2017	16.671