Year	% of revenue
1975	28.1086729362592
1976	29.827315541601244
1977	30.30303030303022
1978	30.634774609015423
1979	30.34482758620693
1980	34.57249070631964
1981	32.8610699936562
1982	33.768214164689866
1983	33.45368525896403
1984	33.983756987659376
1985	32.89462291107453
1986	40.26736631684154
1987	37.73437549169437
1988	37.359449818963185
1989	32.994603686312914
1990	31.886556870206345
1995	34.03238910499543
1996	33.82771299948435
1997	32.566033601121305
1998	34.01182102652016
1999	33.209429465278305
2000	31.942093151476346
2001	32.389226556679134
2002	32.464659434916484
2003	32.810695892115525
2004	32.399346508769575
2005	33.76867224703177
2006	34.09188871347521
2007	32.71817593345776
2008	31.74908561030311
2009	29.177245561184677
2010	31.493287584545527
2011	31.466047405122012
2012	31.48820265371002
2013	29.231986921250957
2014	30.41915192492266
2015	31.616825984673174
2016	32.55500278675873
2017	33.043324368992764
2018	33.00406256409236
2019	32.89676735146909
2020	31.119480388314823
2021	31.184650038348792
2022	31.80330500854311