Year	% of revenue
1998	23.912514162635123
1999	23.48894615499152
2000	23.227794636061013
2003	20.713908985730253
2008	18.412477161169345
2009	21.091309551560563
2010	16.981518811458983
2011	15.728312463412063
2012	19.730478541307267
2013	16.203278800376197
2014	24.26930759599394
2015	24.964923860137723
2016	23.677525370224256
2017	27.050863696461295
2018	26.566032532633894
2019	21.835420338289797
2020	21.73045195670704
2021	21.828903380672607
2022	23.39502984220071