Year	% of revenue
1972	2.8940568475452193
1973	3.4325744308231174
1974	3.755416466056813
1975	6.820929027801761
1976	5.560655737704918
1977	6.088422630198576
1978	7.584760573226144
1979	7.981113395780977
1980	5.935726863627471
1981	6.398623042894025
1982	7.238229746429667
1983	9.364745429391386
1984	10.264157970020905
1985	11.519680828922638
1986	10.838952748914114
1987	7.878575539019825
1988	9.796906138964163
1989	10.220096626753467
1990	10.600479398989178
1991	11.117839492089196
1992	10.572647431975792
1993	11.199713749521004
1994	11.432470379508562
1995	12.213872691160542
1996	10.54290071123907
1997	10.136461357598904
1998	10.157079855344103
1999	9.418038261661842
2000	8.631565825927265
2001	8.976954114617312
2002	7.876791592269126
2003	7.023233312678349
2004	6.016895113857354
2005	13.114573151838012
2006	14.54326802828464
2007	15.570123611414473
2008	27.74704968708899
2009	34.23890939739001
2010	24.4491643196797
2011	25.401483132584502
2012	25.083503622443736
2013	23.17036468403866
2014	18.486339286925997
2015	19.917288531868547
2016	11.794675041554243
2017	15.785741579133516
2018	13.8611396314722
2019	13.065255040229312
2020	12.142294405606654
2021	12.359477391554435
2022	16.346815390256385