Year	% of revenue
1998	11.292414584229531
1999	10.799096854958467
2000	11.095798565768208
2001	12.19622054525261
2002	12.664122667970666
2003	13.311865989175002
2004	11.665249332792241
2005	9.997973261328312
2006	8.374100365480789
2007	7.994761679699036
2008	9.162490534831518
2009	9.064021377684726
2010	9.036626015549407
2011	9.044420340051156
2012	8.591051189110956
2013	8.641309403790636
2014	8.404613485471668
2015	8.594784723743093
2016	11.026328419279778
2017	11.017288530165798
2018	11.04239748397242
2019	13.153655063455602
2020	11.862420037227272
2021	11.92653841102938