Year	% of revenue
1997	16.769629522607143
2002	16.95686320362381
2003	15.893508782338387
2004	17.48800532107958
2005	15.28381596509862
2006	14.990575558720959
2007	15.590833721414082
2008	15.820578546065505
2009	19.347705119349143
2010	21.41079972860168
2011	23.12447219695843
2012	22.583048386198193
2014	14.934124253858691