Year	% of revenue
1990	19.403962271216823
1991	17.853261626772927
1992	17.461307885238885
1993	19.49620774402348
1998	19.799931520527043
1999	20.952073244707723
2001	20.93575242754516
2002	20.453855165531305
2003	21.64260284073068
2004	21.13257298826566
2005	20.2990986208474
2006	19.853234923838155
2007	20.859243808176036
2008	21.261049232239817
2009	21.869644125156107
2010	25.016119251809755
2011	24.4860630217782
2012	22.32464756547575
2013	24.454178828723553
2014	24.86199895049945
2015	24.86637239560033
2016	25.889239097561216
2017	24.412106814781083
2018	26.722591281170445
2019	26.298364908180982
2020	27.259227340141504
2021	28.1639454318586