Year	% of revenue
1997	15.944637952409481
1998	14.983755356090292
1999	14.729575284236056
2002	15.948434070667197
2003	14.51587183465876
2006	14.194838632969521
2007	12.989610328496473
2008	14.103367889373574
2009	15.516623838038072
2010	14.898305635502036
2011	13.423538479296132
2012	13.691384644229867
2013	13.992293743844767
2014	16.251257003304122
2015	18.520493536080394
2016	17.507237150389653
2017	17.264224936985794
2018	16.322439594606074
2019	16.84398611806422
2020	16.360141960021462
2021	17.570438024496898
2022	14.504197246622976