This graph estimates the extent to which a recent spike in cases in Hampshire County is attributable to cases reported by UMass Amherst. It provides another example of why it would be useful for the state to disaggregate higher ed data in the local figures (see this paper on the positivity rate issue). A more recent graph is available on this page.
The graph shows totals for the two weeks ending at the date shown on the horizontal axis. The blue line is from the Mass DPH data. The aqua line is based on subtracting the UMass number from two days before for each Mass DPH date. For the two week period ending Feb. 7, the Hampshire total is 928, and with UMass subtracted it is 425. This gives us average daily new case rates per 100K people of 41.4 and 20.9 respectively, if we assume populations of 160K and 145K for each one (see below on estimating the population being tested at UMass).
The table shows the data from the last two weeks. The first date in the Dates column is the one for the Hampshire MassDPH data, and the second is the one for UMass. In the past, the MassDPH dates seemed to be about 2 days earlier than the UMass ones. This works roughly here too to line up the data. Note that the first two dates in the earlier period no data were reported for UMass. Note also that some UMass cases may be non-Hampshire County residents.
Over the later week in the table, UMass administered 19,668 tests, and over the earlier week, 15,558. Students are required to be tested twice weekly, and non-clinical faculty and staff are required to be tested once a week. If we assume that 1.75 tests are being administered per person, the population being tested in the last week would be 11,239 people. That means that the new case rate would be 521.1 per day per 100K over the last week (410/7*100,000/11,239). If the population is being tested on average once a week, the per capita new case rate estimate goes down to 297.8. Hampshire County as a whole is at 55 over the last week, according to the NY Times. If we subtract the UMass data for the last week, and use a population of 145K, we get an average daily rate per 100K of 21. Obviously, all of these per capita rates would be better calculated using better estimates of the UMass population being tested, but those do not seem to be publicly available.