Dear All, I' ve used ANCOVA (through lm(Y~factor*x)) to study the influence/differences between levels of factor upon the Y-x relationship. I found that both intercepts and slopes differ among levels of the factor. I understand from the results of summary(lm(Y~factor*x)) which of the intercepts/slopes per level differ from "the reference level". I later used lm(Y~factor/(1+x)-1) to obtain "explicit" coefficients per level. My question is: Can I test for differences among all intercepts and /or slopes per levels using simtest (from package multicomp) as summary (simtest(Y~factor+x,type="tukey"))? The outputs seem to contradict the results from the "explicit coefficients approach"! Thanks in advance, Eduardo