Year	% of revenue
1997	29.84840686235414
2002	29.598739519967232
2003	33.49928369662196
2004	30.60904508214511
2005	27.662840197445494
2006	29.397829777804105
2007	28.26717435128395
2008	23.648136677431015
2009	29.65465421882866