Year	% of revenue
1999	30.75541678404758
2000	48.6099348372236
2001	43.365846390399476
2002	43.71913401908203
2003	42.67834793491865
2004	49.91302337359214
2005	55.982644271084794
2006	43.188394596098554
2007	39.10553330550844
2008	48.74125084669226
2009	54.761160354552786
2010	34.14945364821995
2011	27.610670117733488
2012	31.918871682315164
2013	29.738569721462245
2014	30.661610382016814
2015	40.247202765295576
2016	42.410879871617844
2017	39.413852761160975
2018	32.77780778491251
2019	34.75581933208944