Year	% of revenue
1998	18.57111163295782
1999	17.94550920788431
2000	17.905001032478296
2001	19.172144050363897
2002	20.06045413325667
2003	21.125287249696672
2004	21.050731902947664
2005	21.107646715390963
2006	21.2045806774382
2007	22.93506014471959
2008	23.683201371500758
2009	26.700224911641858
2010	24.178679414603895
2011	24.467320070810956
2012	24.558979827992808
2013	25.849886158436053
2014	27.07384050383442
2015	25.292457683935396
2016	30.99302850612837
2017	27.050863696461295
2018	27.331559211322126
2019	27.151926375640013
2020	27.968764607240903
2021	28.69818694503396