Year	% of revenue
1997	18.31025849847676
1998	19.155515524507827
1999	17.866179902499127
2000	17.790193000277032
2001	16.9173680452316
2002	17.20604514569262
2003	18.11317525145036
2004	17.94494266720207
2005	17.72001326721782
2006	18.658706118346398
2007	18.135179817180305
2008	17.446648869002107
2009	21.051047206530214
2010	20.71586417179141
2011	19.504229126538817
2012	20.54469852437462
2013	18.829905137059313
2014	19.775110793330906
2015	21.418712190348206
2016	23.367748249520076
2017	22.10836042400915
2018	21.660026231512653
2019	22.380958896706677
2020	26.657550204795967
2021	20.01548681222581
2022	28.381744910283135