Data current as of 7:21 PM 5/28/2020
May 30 Update — As you read information about the number of people found be infected, it is important to keep in mind the way the information is being reported.
For example, many sites seem to show “the number of cases is increasing” in Wisconsin or other locations. While this may be true, it is also true that more tests are being performed. An apparently increasing number of cases being reported could be occurring because more people are being tested, not necessarily because the infection rate is increasing. So, the number of people being tested — and whether this is increasing, stable, or decreasing — should be kept in mind when looking at a chart or information that shows the “direction” the number of cases is going.
The following chart is an effort to demonstrate this. It shows the number of cases being detected in Wisconsin, which clearly is increasing from week to week. It also shows the number of positive test results relative to the number of tests results being reported. That is decreasing, and is around 5%.
A report or chart that shows whether new cases are increasing or decreasing does not give a full picture of whether the rate of infection is increasing or decreasing, unless you know how many tests are being done. And even that does not fully show what is happening in terms of the overall infection rate, since it may be unknown who is or is not being tested: generally concerned citizens, those who may be at higher risk, or people at home clearly with symptoms who have not gone for testing.
May 28 Update — Wisconsin appears to be continuing a downward trend in the number of positive tests relative to the number of tests over the last week. at 5.1% as of 5/27. Dane County appears to be remaining stable in the number of positive tests relative to the number of tests given during the past week, at 1.1% as of 5/27.
Wisconsin had the highest number of positive tests on any single date on 5/27, at 599 (prior highest number of positive tests was on 5/20, at 528). 5.8% of all tests given on 5/27 were positive statewide.
The number of positive tests per 10,000 population remains about twice as high in the rest of Wisconsin relative to Dane County. 27.8 positive tests per 10K population were reported in the rest of Wisconsin on 5/27, and 13.36 positive tests per 10K were reported in Dane County on that date.
Source: Wisconsin Department Of Health Services website and databases at https://www.dhs.wisconsin.gov/covid-19/data.htm.
May 21 Update — Updated impression from the data: Dane County appears to have stabilized in the percent of positive tests reported. The pattern has remained very consistent for the last three weeks. The positive test percent has continued between 1-2% since 4/28, based on a 7-day average (specifically 0.9% at the lowest to 1.8% at the most). During that time period the number of tests reported ranged from a low of 233 per day (on May 2) up to 1425, which just occurred today (also the greatest number of tests reported in Dane County on any single date thus far).
Data suggest that the rate of positive test results could have stabilized and may well remain within this 1-2% range for the foreseeable future. A weeklong increase to 2% or more of positive test results might be considered a potential signal of an increasing infection rate in Dane County. Other factors might also contribute to such a change, but the 2% threshold could well be a useful metric.
This shows the total number of cases (positive test results) that have been reported in Wisconsin and in Dane County. This also shows the differing patterns of increased cases between WI and Dane County. WI seems to have begun more slowly, with an increasing rate up until the present. Dane County appears to have begun more quickly, with a possibly slowing rate of increase at this time.
However the total number of cases and number of new cases each day may be misleading, simply because more tests are being done. So, the proportion of positive cases relative to the number of tests being done may be a more meaningful measure. That is what the chart below shows, taking into account the 7 days up to and including the date shown.
It appears that, about 4/27 to 4/28, Dane County showed a substantial reduction in the number of positive cases relative to the number of tests done, from 3.5% to 1.5% (which would have begun during the preceding week). Since that time, Dane County has remained below 2% in terms of detected cases relative to number of tests administered, dipping just below 1% (0.9%) at best on May 7, with what appears to be a somewhat increasing trend, up to 1.8%, on 5/13, since that time. Dane County continues to remain below 2% positive test results of people tested, on average per week, since April 28.
A reduction in the number of detected cases in Wisconsin overall appears to have begun to be detectable about May 7, with a reduction that would have started to occur the week before, from a weeklong average over 10% (10.2%) on May 6, dipping below 10% (9.5%) on May 7. Since that time, WI seems to be showing a decreasing number of positive cases relative to the number of people being tested, to a low point up to this time of 5.7% for the week up to and including May 18.