Year	% of revenue
1990	31.496629553889267
1991	34.82624254473161
1992	32.37483778430435
1993	35.394562334217504
1994	27.42779060453282
1995	27.175239433494802
1996	30.932985426080318
1997	30.639721096340804
1998	29.322347310599877
1999	26.22791293213829
2000	27.953928066934697
2001	26.529802075653603
2002	28.412296827505866
2003	34.49973007433337
2004	32.2118090735112
2005	34.38358789272365
2006	31.715951755139553
2007	30.396162363645796
2008	29.419360827784214
2009	29.497489222963146
2010	26.110698380901688
2011	28.332459156498835
2012	25.728455615385965
2013	21.667464552937908
2014	22.78405983591465
2015	20.903971491828273
2016	19.651186706543402
2017	15.304390712693012
2018	17.904981141599496
2019	14.498150581356944
2020	21.64240551558944
2021	15.515785112077959