Year	% of revenue
1972	7.237851662404088
1973	7.355202460276784
1974	6.944737619791452
1975	7.933560301248313
1976	7.161237339173282
1977	8.043132402333391
1978	9.360652534922348
1979	10.02227657901633
1980	9.250576624947996
1981	8.928571428571418
1982	9.799160071993866
1983	10.190196579014543
1984	9.851041807299408
1985	9.631282245373592
1986	10.926202226558026
1987	11.620083926165577
1988	10.302769616598747
1989	10.112431820520767
1990	11.087542210681569
1991	11.93476227788591
1992	13.437096445320462
1993	18.115815096915252
1994	14.170599746748024
1995	16.887240643785145
1996	14.0203785953495
1997	12.306900102986612
1998	11.826079727314296
1999	10.215064681870798
2000	11.721631492776309
2001	12.776632918197295
2002	12.28820900176709
2003	12.290204060510927
2004	12.747081453966569
2005	12.53498727735369
2006	13.415092920021065
2007	14.230493513065234
2008	15.434785556414324
2009	14.467937189233304
2010	14.274503997631033
2011	13.820499979697631
2012	13.212459076745073
2013	12.835121501549176
2014	12.69776978963623
2015	12.655031286153234
2016	12.076813143262036
2017	12.16345755571072
2018	12.298172233999885
2019	12.583789348821073
2020	12.263962960792357
2021	11.889894500080329
2022	11.270186117757778