yes, I know it sounds odd - but the requirement is to understand how many times a case is logged under each category (but not count duplicates) and then how many this represents in total.
It's a database of antisocial behaviour and one perpetrator (case id) can appear several times under different categories- (under 'noise', 'neighbour nuisance' etc) and have several individual incidents within those categories , but the requirement is to understand in total what categories cases fall into.
That probably sounds like gobbldygook.
I've tried using the formulas within the format field function but have to confess that I ddon't really know too much about how they work.