Year	% of revenue
1998	12.238588404472871
1999	11.716104670823661
2002	14.778496116631231
2003	14.165448173913227
2004	14.223899232982186
2005	14.746725728384778
2006	14.08521724514665
2007	13.786519458921093
2008	15.305421507473493
2009	17.07685289896824
2010	13.143060202058743
2011	17.554667580376552
2012	17.572697432454596
2013	13.801208241660873
2014	15.788449287150652
2015	16.752500627683105
2016	17.239668475173502
2017	15.354622513373506
2018	17.074721092216226
2019	17.71571157831136
2020	21.804703365039614
2021	19.851973716608946