Year	% of revenue
1998	18.900302495588605
1999	21.98480794661254
2000	16.668929130580366
2001	14.133364133364134
2002	20.453855165531305
2003	21.536665513663092
2004	21.050731902947664
2005	24.037868620552068
2006	24.40622195632665
2007	24.465738839455472
2008	23.683201371500758
2009	26.700224911641858
2010	25.422737683348767
2011	24.288701054902077
2012	23.031282986438896
2013	25.849886158436053
2014	25.917508936684097
2015	25.61999150773307
2016	28.27435681884666
2017	27.140574775898507
2018	27.331559211322126
2019	28.173717708723323
2020	29.853664791396195
2021	25.407026065937643