Year	% of revenue
1972	10.042036431574031
1973	8.72048743335872
1974	8.138417173982699
1975	8.867276887871855
1976	10.030395136778116
1977	10.077669902912621
1978	11.437677053824363
1979	11.563828228052177
1980	10.26553169864058
1981	9.572176054170514
1982	9.657265262406284
1983	10.596874733156861
1984	12.508219478337107
1985	15.179681487182522
1986	15.424040228217775
1987	18.41847866977654
1988	15.00203832042397
2001	13.697402293470631
2002	15.550208936740601
2003	14.844063904176677
2004	15.138589381847856
2005	16.027654901430417
2006	13.553607552258933
2007	14.502194081294887
2008	13.172895157772285
2009	13.39001358962566
2010	15.662821713811411
2011	20.579566665892145
2012	15.172405205155345
2013	14.68537231097024
2014	14.753992596895515
2015	13.645131310394051
2016	13.792395717960378
2017	13.095256116331017
2018	12.433357671342533
2019	12.311047355597008
2020	11.925955292785998
2021	9.745576334752283
2022	9.288389877037117