Year	% of revenue
1972	8.549091278302386
1973	9.214378659726716
1974	8.600055663790691
1975	9.447415329768283
1976	8.55007723458439
1977	8.79027997886952
1978	8.328079325958587
1979	6.763081531405011
1980	7.892279250605134
1981	6.23658061616816
1982	7.4781152120787935
1983	6.427271888859999
1984	6.057748538011683
1985	6.591243872401052
1986	6.253869674137719
1987	5.622628913818644
1988	3.7124328698856006
1989	4.176093388131032
1990	4.007726973439812
1995	2.719214941437164
1996	2.6488054136169037
1997	2.5989696941569593
1998	2.6085167660975106
1999	2.4441675452889866
2000	2.3725181870021252
2001	2.2996410480056357
2002	2.1006063113671445
2003	1.9187409475743231
2004	1.8446829322054912
2005	2.023697871946951
2006	2.023082804402966
2007	1.828494499067545
2008	2.0694900751101297
2009	2.005481800647439
2010	1.6806440791680644
2011	3.5764119221355535
2012	3.7447348681553283
2013	4.4947755530908875
2014	4.30986300349012
2015	4.58797273070966
2016	4.426916791018262
2017	4.4808560441397765
2018	4.271503803393798
2019	4.1636086161301975
2020	3.991880067077707
2021	3.7470139915823
2022	3.284489134997901