Gary, Thanks so much for your reply. I watched the tutorial and changed the categories to simple weighted mean of grades (while leaving parent category as weighted). This now allows me to use aggregate only non empty grades. Another tutorial I saw told me to set categories to sum when using weighted. That option doesn't allow for aggregate only non empty grades apparently. http://tinyurl.com/5l6rbw
Would you say that is correct... one cannot use sum and weighted together if we want the non empty grade option?