Year	% of revenue
2008	19.197145005761698
2009	22.43153050015527
2010	22.620071597668872
2011	20.4006228028042
2012	20.12750466994456
2013	21.667464552937908
2014	21.405494392416056
2015	20.73949545908012
2016	19.690933037047984
2017	19.902675579652797
2018	19.173897251322444
2019	19.867153640727206
2020	18.83910496184148
2021	18.41218641758527