Year	% of revenue
1999	1.9943370746875646
2000	1.5626257467367788
2001	3.2383770647421435
2002	4.511369125501044
2003	4.465340779887461
2004	4.638913232007399
2005	4.231182643000533
2006	2.253962298358426
2007	2.6332137726114255
2008	3.791523199367803
2009	8.566559226430298
2010	3.7823868801365417
2011	2.397957549315446
2012	2.5138081625095405
2013	2.640706882682181
2014	4.11500237570181
2015	4.9805153136972224
2016	3.436294744735782
2017	3.6284888316220467
2018	2.7067226485154148
2019	2.872464163692351