Calculating # applicants received/reviewed per hire

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HI! Does anyone have a way to calculate how many applicants were received/reviewed per hire (or group of hires by job function) in a given time period?  I found a way to do this for "filled" reqs, but we have many "evergreen" reqs and a fair number of multiple positions on a single req that remain open until the last position is filled.

Thank you in advance!