Year	% of revenue
1997	8.89086990109027
1998	9.07991063030537
1999	10.880224907432641
2000	11.961837184773229
2001	14.695525611531057
2002	13.492034017900249
2003	12.671703852314462
2004	12.96944416667857
2005	15.28381596509862
2006	14.990575558720959
2007	15.590833721414082
2008	15.820578546065505
2009	15.48520248015817
2010	17.566502125325655
2011	18.406198959243362
2012	19.011280439430916
2013	19.119510312626566
2014	19.32281397637278
2015	21.66050368019978
2016	21.331454902556462
2017	20.867928823642227
2018	22.24373781779811
2019	28.8336027085676
2020	29.815534839677248
2021	25.117340763707496