Good catch, most sources and the link I included hold ROI as equivalent to ROA, and distinguish it from profit margin. I was trying to shift to a lay voice in

Good catch, most sources and the link I included hold ROI as equivalent to ROA, and distinguish it from profit margin. I was trying to shift to a lay voice in that bit and in the process totally misused one of the terms of art under discussion, was a bad oversight on my part. I think my general explanation stands as to why we might want to shift between ROA/ROI and profit margin when comparing different industries though.