Reports :: Percentages Of Approved Proposals

I'm creating a report that list multiple users providing an input of "approved" or "not approved" for a plurality of proposals. I'm trying to create a report that lists the percentage for each user that calculates the number of times the user inputs "not approved" over the total number of proposals that particular user reviewed.

For example,

Steve reviews 50 proposals, and of the 50 proposals Steve inputs 10 of those proposals to be "not approved". I need a calculated field that counts the number of times that Steve inputs "not approved" and calculates that 20% of proposals reviewed are not approved, of all the proposals he reviewed. The number of proposals are continuously being added so the number 50 will not always be the denominator.

There are at least 10 other users that I have to do the same calculation but if I'm able to do the example above.