Year	% of revenue
1998	18.982732428013126
1999	19.896318015393412
2002	20.27007593997685
2003	20.064750473783953
2004	19.334539559697244
2005	19.773064276964735
2006	19.853234923838155
2007	18.011004783080732
2008	20.49340061810691
2009	21.494690222178722
2010	23.113411664956637
2011	22.660485954404045
2012	22.17836810362502
2013	24.032171182728938
2014	24.15175054600278
2015	24.112753283467594
2016	23.859145366582112
2017	23.872198725992906
2018	24.501440335230722
2019	24.19226767246363
2020	25.29115662021254
2021	24.896076824140074