Year	% of revenue
1990	3.9729222132788475
1995	2.5170509905813576
1996	2.5346347607052895
1997	2.3529411764705883
1998	2.4119850187265914
1999	3.67504835589942
2009	1.8804733727810652
2010	1.9952019431531969
2011	2.679528403001072
2012	2.951697855676724
2013	3.4262835319123752
2014	3.162648430260991
2015	2.60395247063036
2016	3.0797518649728963
2017	2.987756208954948
2018	2.4756134722407066
2019	2.0964789670174193
2020	2.1817087480780124
2021	1.9930789832133466