I think you could use "of" or "for" in this case. I suppose strictly speaking it is "of", but no one would fault you for using "for" here. You could say, "The results for this group were different from the results for this group..... or.... the results of this group were etc. Here is something though: used is the preterite tense of the verb to use if you want to make a question out of this tense you say "did you use" So, "Why did the author use 'for' rather...... in the sentence below. Oh, I see now too that the adjective "below" comes after the noun. Ha, ha, ha. How annoying!! So...... the sentence below The reference below The plug in below the desk etc. Dave