Year	% of revenue
1990	18.9447488393492
1991	17.261951797708416
1992	18.249279103063056
1993	19.893336903646183
1994	23.861925772125616
1995	16.98848175345734
1998	18.982732428013126
1999	20.74793074032232
2012	24.11634261703623
2013	24.612755724800824
2014	24.932040138268956
2015	27.59552687590797
2016	24.040765362939965
2017	20.389275832458733
2018	21.153684572794965
2019	21.269802670899935
2020	24.434007903702202
2021	21.769217900004598