Year	% of revenue
1972	1.7838874680306933
1973	1.5325474115838031
1974	1.0976484991767648
1975	0.9044327521579145
1976	0.7829181494661928
1977	1.1086138538851975
1978	1.5067890983686592
1979	2.116275006551932
1980	2.264907172836234
1981	2.504160266257041
1982	3.062594634745607
1983	3.8881797293847282
1984	4.250483776607729
1985	4.52281827055239
1986	4.022283237249377
1987	4.083891839939596
1988	3.771315258043115
1989	3.1606977462179726
1990	2.8812980775091726
1991	3.6549301114677926
1992	5.159938953183034
1993	10.851851628140158
1994	12.741452745481768
1995	8.733275159976731
1996	9.540887822720471
1997	9.839699099986566
1998	8.355156503304652
1999	7.30488820292033
2000	6.437451647145608
2001	6.36502105546098
2002	5.107238141436541
2003	4.69183930450382
2004	4.341337224728044
2005	3.967875318066158
2006	3.5587991874200586
2007	3.2891500217871052
2008	3.2013993410080133
2009	3.405020629618994
2010	3.575658868818478
2011	3.4771192290513375
2012	3.5604875290900244
2013	3.205899674800912
2014	3.1541908209503076
2015	2.959433739286203
2016	2.7393805469153447
2017	2.550326039361413
2018	2.3365610496762734
2019	2.1508264231599914
2020	1.8449276211686103
2021	1.2659990360413431
2022	1.310533323989067