Year	% of revenue
1988	16.833937614801528
1989	15.399686617570044
1990	14.564272576888495
1991	14.121000875311452
1992	13.72379713299786
1993	14.577756063274835
1994	12.221437515335747
1995	12.825701077003652
1996	12.439565682217012
1997	12.56150746193706
1998	12.57670229074711
1999	10.926448208228996
2000	11.114006333769739
2001	8.435986727633003
2002	8.293533221828774
2003	7.5015223413656535
2004	7.482545498490687
2005	7.341952804026735
2006	7.015947226225119
2007	7.23451779408698
2008	6.559220743165555
2009	6.242696318696254
2010	6.454520666209661
2011	6.906589631008551
2012	7.096245044915543
2013	7.189179313284292
2014	7.22041267464181
2015	7.303782347963668
2016	8.232264869755893
2017	8.828181867669594
2018	8.388826989403428
2019	8.658260468343862
2020	8.833726830712783