Year	% of revenue
2001	25.779595918664675
2002	24.340207079353945
2003	25.485751919713895
2004	23.55184777795237
2005	28.286553524804177
2006	23.626766009715347
2007	25.712511702723095
2008	24.5258827754622
2009	23.269216739453455
2010	22.798936196496495
2011	27.519722716957926
2012	26.06282604658759
2013	27.04092230799266
2014	23.587818698622584
2015	21.670994060726734
2016	20.016243582261257
2017	22.815816186324543
2018	20.91461705667446
2019	20.13356915852502
2020	19.167320740674818
2021	18.821958579566363