Year	% of revenue
2008	20.877038641131488
2009	22.774472759081096
2010	22.969074738032532
2011	22.892130624285873
2012	20.929453655817927
2013	23.010066458257555
2014	22.33360288103329
2015	20.73949545908012
2016	19.690933037047984
2017	19.902675579652797
2018	19.173897251322444
2019	20.11072039964929
2020	18.946196770851515
2021	18.227494486711088