Year	Percent
1981	4.38833
1982	4.07479
1983	4.02498
1984	4.0522
1985	4.20183
1986	4.46458
1987	4.46338
1988	4.52625
1989	5.1175
1990	23.0563
1991	22.52189
1992	22.41292
1993	19.66235
1994	17.78714
1995	17.29727
1996	16.00122
1997	16.91067
1998	17.61693
1999	16.94809
2000	17.87382
2001	16.50187
2002	16.45037
2003	17.16276
2004	17.13697
2005	17.24996
2006	17.72768
2007	17.40509
2008	16.84102
2009	15.40496
2010	16.57185
2011	17.98683
2012	17.88155
2013	17.55313
2014	17.89663
2015	18.87618
2016	16.80889