Year	% of revenue
1991	22.664543524416136
1992	20.573927571126728
2009	24.816906697326267
2010	21.645807920509384
2011	26.244133841044263
2012	24.012221645736922
2013	25.822437201856214
2014	26.651368606366
2015	27.812830378160662
2016	30.03661358028788
2017	29.384816648490887
2018	32.67171396607715
2019	29.86534452031335
2020	28.423218403900144
2021	29.77586644494676
2022	32.0337044434803