We would like to adjust our ANOVA-type analysis by using the covariate "age". Because limma is based on contrast, rather than "type III SS", it seems to me that the only way to proceed with an ANCOVA-type analysis is to orthogonalize the design matrix against the covariate. Is there a more straight-forward method? Naomi S. Altman 814-865-3791 (voice) Associate Professor Dept. of Statistics 814-863-7114 (fax) Penn State University 814-865-1348 (Statistics) University Park, PA 16802-2111