Year	% of revenue
1972	38.92780992994208
1973	37.69518542615496
1974	34.98469245755649
1975	36.32464349376111
1976	37.247943890118215
1977	37.84469096671956
1978	37.80019487590978
1979	36.817841430309706
1980	33.33587451638114
1981	34.54003761588512
1982	34.11043930198138
1983	32.76013850578083
1984	37.14692982456151
1985	37.09038661225265
1986	40.34938990122211
1987	41.76327401208128
1988	41.597776586719895
1989	42.562818779367895
1990	44.45059322967514
1995	34.74200696422919
1996	34.29084380610413
1997	32.357172692254146
1998	30.42583830487554
1999	31.86235981980255
2000	30.574899345095126
2001	31.228823509678282
2002	32.478238036887916
2003	31.32101954577354
2004	30.010883491534297
2005	30.190349127511457
2006	31.25523368002039
2007	31.189238697432163
2008	30.975797847054228
2009	30.822157302863847
2010	31.569942972156994
2011	31.584966946496785
2012	31.061104379435694
2013	30.563306286848402
2014	32.333908809757425
2015	31.936534263448664
2016	32.91172221037921
2017	33.53595910860582
2018	33.74722059684026
2019	34.24434115029299
2020	31.827867508920576
2021	32.67546354225913
2022	36.68812346320692