Hi Nancy,
Natural weighting is the assumed aggregation method. If any other method is selected, it's noted in Categories & Items and on the User Report. In Natural weighting, the "natural" refers to the underlying weight of item points divide by total points, where no item's weight is artificially inflated. To change the weight of a category or item, simply check the box, and adjust it to the percentage you want. Note that all categories in Natural redistribute to 100[%].
Simple Weighted Means doesn't transfer as well, since it is, in essence, rescaling a category. There are workarounds to achieve the same thing if it's absolutely necessary.
Mark