Year	% of revenue
1972	15.626320980696068
1973	16.969225449515907
1974	16.95214790647091
1975	17.341624149659864
1976	18.60897145446307
1977	17.42078289827906
1978	17.050599080016728
1979	16.245375120480055
1980	15.484832930018822
1981	15.164276048714479
1982	16.257226106141143
1983	16.84646936885282
1984	16.938760373486726
1985	16.706682374696154
1986	17.589995074630064
1987	22.17210872553075
1988	21.976712148256404
1989	21.796318636416704
1990	20.09026224440922
1991	19.841037420724618
1992	20.381109060997446
1993	21.521032644416856
1994	20.969699523789455
1995	18.686219086715088
1996	18.751022753306447
1997	18.371560339780395
1998	17.608138492743596
1999	17.733618711464306
2000	17.470463763004762
2001	17.651466067281515
2002	17.624301475856143
2003	18.375801255690718
2004	18.53740629302871
2005	18.13577011289023
2006	18.404360612225403
2007	18.05932606328318
2008	18.126679350532555
2009	19.25796651540223
2010	16.013462782330016
2011	18.458337675217486
2012	18.31351490245304
2013	17.842931832528578
2014	17.98084057014175
2015	18.139141554122155
2016	18.349597262280138
2017	18.520427471602623
2018	18.621768508241168
2019	19.322186038186477
2020	20.333431017284422
2021	19.570511373767577
2022	19.290251341747545