Year	% of revenue
1990	25.628645004923122
1991	24.20675944333996
1992	22.942421965712725
1993	21.800397877984086
1994	24.760872638175567
1995	25.951262803683022
1996	23.3150894164068
1997	23.553754145290668
1998	23.1195953662914
1999	24.373879641485274
2000	23.498859067695317
2001	23.72823682867351
2002	23.04108043173586
2003	21.89612399047032
2004	21.88843859056625
2005	19.042230905620197
2006	18.244528695846558
2007	16.34988095459443
2008	17.457467811799106
2009	16.147515755223786
2010	16.286235515210116
2011	14.461863632454778
2012	15.221372669391192
2013	17.20431015726045
2014	16.80061442987287
2015	16.63159732194894
2016	15.682824620984507
2017	15.75943715912417
2018	15.792458404126593
2019	16.030555142000537
2020	15.813597111788832
2021	19.865286229934117