Year	% of revenue
1976	20.79042939542833
1977	17.15988018038777
1978	20.028544243577546
1979	20.17626921115886
1980	16.48411151335128
1981	16.770824653501094
2001	13.260456273764259
2002	15.712228054965834
2003	11.897319470035974
2004	11.123655594509477
2005	9.913978843007339
2006	9.402574464232114
2007	10.612787247770013
2008	8.660682055827369
2009	15.516623838038072
2010	14.489451077679796
2011	10.629631520287228
2012	10.830313153680533
2013	14.336900958751075
2014	17.763192827594196
2015	24.204600718587805
2016	21.87830757697957
2017	26.786832779908536
2018	22.87435970910034
2019	18.73629286241412