Year	% of revenue
1972	16.81109185441941
1973	13.333333333333334
1974	10.038986354775828
1975	9.407216494845361
1976	8.686257562662057
1977	9.564329475833901
1978	9.353574926542606
1979	10.026041666666668
1980	12.46660730186999
1981	13.69814858214202
1982	13.630379746835445
1983	10.597302504816955
1984	11.453920549916074
1985	11.894016596302228
1986	11.697729152089561
1987	9.832522960561858
1988	9.615214114726482
1989	12.183358167986825
1990	9.28443763564407
1991	10.245354400801157
1992	11.761138325169116
1993	12.43553468585074
1994	13.046462955211386
1995	12.068527560610764
1996	12.605609188752698
1997	13.414150319594444
1998	17.733509127405274
1999	17.150093556194086
2000	17.668925985181176
2001	17.60071940526582
2002	17.998612250237226
2003	17.11061022826472
2004	16.96637144880766
2005	16.22287895213627
2006	16.8478709187798
2007	17.548888091716012
2008	16.329203203049055
2009	16.58610346175525
2010	17.024505729598136
2011	16.98919738092666
2012	23.881712975584932
2013	23.47367851008415
2014	22.204130793031005
2015	21.22940280797386
2016	20.346266250527478
2017	19.32339208351199
2018	18.52852619675863
2019	19.13970548720023
2020	18.726591065269528
2021	17.91162490738856
2022	16.834373853486966