Year	% of revenue
1990	20.239610683620487
1991	22.82984859408796
1992	24.176582869674696
1993	25.65027334679693
1998	18.845521703465455
1999	16.945643313541808
2001	24.555581921724915
2002	23.267593778118957
2003	23.23657861227747
2004	21.752192819306423
2005	23.307548378045695
2006	22.22999514496703
2007	22.484865142861132
2008	23.236896644765217
2009	23.078014716557025
2010	22.798936196496495
2011	25.070835110585158
2012	23.172734447625928
2013	23.62110991883622
2014	23.587818698622584
2015	20.360285279013922
2016	19.667709193275847
2017	19.505922897239962
2018	19.93691793336954
2019	19.988937020188246
2020	19.167320740674818
2021	17.84455054927819