Year	% of revenue
1997	16.769629522607143
2002	16.95686320362381
2003	15.893508782338387
2004	17.48800532107958
2005	19.517587879272714
2006	20.2981857089398
2007	21.502075026430944
2008	21.38464527766296
2009	23.341262041441006