Year	% of revenue
1972	34.33852140077821
1973	32.671629445822994
1974	29.136690647482016
1975	27.765163801492054
1976	26.92110655737705
1977	27.15453973579367
1978	26.006549797726837
1979	25.82330588980367
1980	24.445335471798984
1981	26.605504587155966
2003	44.78196880144024
2004	43.80033352168422
2005	42.272333001120906
2006	42.25816768299882
2007	42.33402332310373
2008	39.781290455295306
2009	39.637566858222236
2010	40.68072684034817
2011	40.66629012635852
2012	41.01730660520938
2013	39.629004314964384
2014	44.263385363730215
2015	47.67481675658692
2020	43.375302439336785