Support Forums : Reporting Question - Results Calculations

I work with a nonprofit canine health related foundation and have developed a health survey for dog owners to complete. I structured some of the question in two tiers, ie, has your dog ever been diagnosed with any type of eye disease, if the respondend answers yes, it brings up another page where they can choose from a list of specific eye diseases. In the reporting function, I would like for the percentage of people answering to be based on the total, not just the count that landed on the page because they answered yes. Currently if there were 10 responses, and only one person indicated eye disease, and the specific disease was PRA, the PRA % currently shows as 100%, it should be only 10%. Any help in how I should modify the question?