Year	% of revenue
2006	34.42615557247336
2007	34.07900312067126
2008	32.40227229552098
2009	31.965638347549728
2010	32.07918240903047
2011	33.57289365539805
2012	34.359459740849765
2013	34.14843898161553
2014	34.0559172786579
2015	34.87797160901218
2016	35.70111438482941
2017	35.9495456293082
2018	36.686482400142665
2019	34.91717990726232
2020	36.19831750561488
2021	36.75166169700279