We average the daily new cases for the seven-day period ending on the date of the latest reported data, then do the same for five preceding weeks. Averaging reduces the variability of daily numbers that may be partly influenced by the number of tests performed on a given day.

The graphic provides a clear representation of the course the disease has recently taken. An upward course does not necessarily predict an upward trend. A downward trend over several weeks may indicate that efforts to contain and reduce the spread of infection are working.

We focus on the county, as the State recommends, because the dataset is larger and more reliable. It is also most relevant, since few people confine their activities to their town’s borders.

The chart above depicts Weston’s case rate as 14-day averages reported each week for the past six weeks.

The case rate is the average daily number of new cases. To allow comparison to other population sizes, it is expressed as an average per 100 thousand of population.

Case rates were comparatively low in the autumn, less than seven percent, and critically high in mid-January, where they reached the low eighties.

We see the case rate as the most relevant indicator of what is going on. We are far less impressed by the positivity rate, which gets all the headlines, especially when it jumps on a daily basis.

This chart depicts the average 14-day positivity rates for Weston, calculated at the end of each of the past six weeks. Averaging the rate over 14 days muffles the daily volatility. But the basic issue with the positivity rate is that one would think it connects to actual cases, but it doesn’t.

When someone tests positive, he or she is counted as a confirmed case once and only once. But every test that person takes, no matter how many, no matter whether positive or negative, goes into the positivity calculation. That is true for all tests. As a result, the figure is more indicative of how much testing is being done than what is actually happening with the virus.