Year	% of revenue
1972	6.22568093385214
1973	5.955334987593052
1974	5.323741007194244
1975	4.930262731106065
1976	4.30327868852459
2003	6.883060717506528
2004	6.267234608198113
2005	5.644545958399714
2006	3.87030442743045
2007	2.5951329860374965
2008	2.4955999149055055
2009	2.895109868510124
2010	3.8942666808945257
2011	5.524876492814335
2012	6.921105151646467
2013	8.940982341358474
2014	7.632188408486506
2015	7.731238811765105
2020	10.629658336403605