Year	% of revenue
1997	24.238570220419557
1998	25.646027775087017
1999	27.94704347950814
2000	23.91648288426503
2001	24.06451007089535
2002	21.25004642180711
2003	23.503810248030156
2004	23.55184777795237
2005	27.03912687008681
2006	34.85266750316644
2007	32.41248039084688
2008	26.244863596293737
2009	23.460418762349885
2010	15.421208693267516
2011	23.546432305997644
2012	22.6255392775381
2013	23.054768873367518
2014	28.346405803424666
2015	26.02821322705354
2016	25.16556483490423
2017	24.053107905850375
2018	20.91461705667446
2019	20.78643632614265
2020	23.165875266038576
2021	18.117459099792413