Year % of revenue 1992 26.577636639271613 1993 26.849619499976207 1994 27.84388664220478 1996 27.034440719292895 1997 28.21210771745556 1998 26.39064122700861 1999 28.171760619864028 2000 30.2209723575052 2001 26.090212831332348 2002 27.82777164140222 2003 32.14952843832401 2004 28.20980842426617 2005 33.81532113261114 2006 36.656763253717514 2007 30.79341257099688 2008 32.00456022609518 2009 32.83293949505896 2010 30.632618029201776 2011 36.237808654522446 2012 33.84524491101992 2013 35.24071951476202 2014 32.586347316696745 2015 31.474029418679628 2016 34.272878914928974 2017 30.91337517999357 2018 31.640169102358374 2019 28.39044401855299 2020 31.14123448411285 2021 31.083319956374588 2022 27.571752368581855