Year	% of revenue
1976	1.858577227088229
1977	1.4714111721913163
1978	2.5467808436409767
1979	3.051933862626557
1980	1.974070979918933
1981	2.5039580034997084
2001	15.950168692764954
2002	16.44469626120376
2003	14.213718522418182
2004	10.953162352532487
2005	8.23437930308283
2006	6.085886587631756
2007	6.471334585339061
2008	5.028733927727096
2009	8.413241377984082
2010	7.073388854731428
2011	6.0968035597301276
2012	5.626154117277471
2013	5.0043563396769
2014	5.0243526475760785
2015	5.5925584360874865
2016	10.250060437874943
2017	8.070563806876196
2018	10.01206852916631
2019	13.153655063455602