Year	% of revenue
1972	9.864968865878396
1973	9.85958485958487
1974	9.793678433855694
1975	10.141612730546472
1976	10.207322452580499
1977	10.860155819626979
1978	9.434157442846782
1979	9.186178247734135
1980	8.937114531096888
1981	8.481932751137384
1982	8.5469225545187
1983	8.303802317785653
1984	7.772939142613295
1985	6.985633873813326
1986	7.08814956277012
1987	7.281882444078626
1988	7.955912183388094
1989	8.205233664078959
1990	8.320468543599702
1991	8.371177049806732
1992	8.205230851347741
1993	7.9310168101681136
1994	6.46099334107154
1995	4.192319159646093
1996	4.021460419567205
1997	3.955577810297016
1998	3.9754675684604655
1999	3.8940731477445194
2000	3.873008950746959
2001	3.787546790969191
2002	3.7993648103684117
2003	3.831888556357383
2004	3.746045084862817
2005	3.664751414881478
2006	3.6763705030826435
2007	3.686087777924492
2008	3.886115935163599
2009	4.105679873322284
2010	4.100527854546061
2011	4.018857844919255
2012	3.995543102936257
2013	4.491977935839785
2014	4.221898259168722
2015	3.985825301249109
2016	4.053315720812294
2017	3.751792988236813
2018	3.5644917669959364
2019	3.4782581111953426
2020	3.527811659146659
2021	3.5423356601302
2022	3.437503147830767