Year	% of revenue
1981	18.52207293666027
1982	16.001823569637565
1983	17.68833849329205
1984	17.58221225710015
1985	12.975682197883796
1986	16.199736321687542
1987	17.73167777104785
1988	15.647550322825673
1989	18.182802685726664
1990	17.903969617506103
1991	22.46530612244898
1992	16.234887737478413
1993	17.073314474304574
1994	16.885562530178657
1995	16.051944986220143
1996	17.791095061787303
1997	18.04475651436339
1998	17.937517165421543
1999	19.43816262360629
2000	19.730064437668112
2001	21.07852690627911
2002	21.499217942916257
2003	19.52427032484337
2004	17.867154990094875
2005	18.485419681534704
2006	19.425190351465993
2007	20.487777187293958
2008	24.70594478080623
2009	22.85401388647519
2010	19.066707419139085
2011	15.463598800252479
2012	15.377636963834524
2013	14.770153794610968
2014	15.22619790406148
2015	15.179283564105775
2016	16.890217279366524
2017	16.964372031449937
2018	15.906912018428388
2019	15.898381153815999
2020	16.300404010652976
2021	14.399657848962025
2022	17.177130297212123