Year	% of revenue
1997	34.16402032660654
1998	37.59484574033242
1999	38.29627624260888
2000	38.80325828886395
2001	36.448294265960776
2002	36.07239218323032
2003	38.490853735701776
2004	38.76711803047564
2005	36.920884760232155
2006	39.155851966704844
2007	42.03197614697237
2008	38.285686494298126
2009	39.10963538798055
2010	39.987654632099925
2011	39.453504671744646
2012	40.70030323710566
2013	40.16896406338975
2014	38.31755898616665
2015	39.64044401485693
2016	38.53404490149007
2017	38.5566454922251
2018	40.7160099023625
2019	40.412862857512756
2020	39.839493148833455
2021	39.839493148833455
2022	37.71284633963277