Comparing two sets to find missing/added values (with formula?)

    I have a dashboard that loads files from consecutive Fridays showing a list of patients.

     

    Relevant fields:

    ReportDate     Patient ID

     

    What I want to do is count how many patients are on the latest report date, but not on the report date 7 days prior.  This will show me an estimate of the number of admissions during the week.

     

    I also want to show how many were on the report 7 days prior, but not on the last report date to show the number of discharges in the week.

     

    Will I need to do some kind of interval match in my data load, or is this something I can do in a formula?  All I really need for now is the two values in KPI boxes.

     

    Thanks.  You are all amazing.