Year	% of revenue
1973	4.34063662670525
1974	5.046007717423568
1975	4.950099800399202
1976	3.3185185185185184
1977	4.067562909341606
1978	4.586056644880174
1979	3.6544317999679437
1980	4.128938790293372
1989	4.952362683036
1990	5.376529381354471
1991	3.0021641753485326
1992	1.730813026645411
2014	6.047680487056582
2015	6.177566779806176
2016	8.200181336828528
2017	8.423920183219732
2018	7.8414113777532535
2019	7.755717856216792
2020	8.436562000929898