Data Update

Massachusetts Data Update September 10, 2020

Testing positivity rates continue to gradually increase, with a 7 day trailing average rate of 2.0%, the highest rate since early August. Once again, this is at odds with the headline positivity rate of 0.8% announced by the state. Tests of people previously tested are now over almost two-thirds of all tests, and these repeat testers have a positivity rate of only 0.2%, the lowest on record.

Massachusetts Testing Statistics
7 Day  Trailing Average
September 10, 2020
Testing Statistic   Current 7 Days Ago 4 Weeks Ago
Test Positivity Rate (Individuals)   2.0% 1.6% 1.7%
Test Positivity Rate (Include Suspected)   2.1% 1.7% 1.8%
Test Positivity Rate (All Tests)   0.8% 0.9% 1.5%
Test Positivity Rate (Newly Tested)   2.0% 1.6% 1.7%
Test Positivity Rate (Repeat Testers)   0.2% 0.3% 1.0%
Percentage Repeat Testers   66.4% 53.0% 30.8%
Newly Tested (Lagged 1 Week)   19,735 19,520 14,493
All Tests (Lagged 1 Week)   42,015 34,815 20,766

Hospitalization statistics are stagnant, although there are slightly fewer patients in the ICU or intubated compared to four weeks ago.  Unfortunately, the number of patients hospitalized has increased for four consecutive days.  Since the last data update, I’ve converted the hospital measures from current day only to a 7 day trailing average, consistent with the other tables presented here. I’ve also added two additional measures: the percentage of hospitalized patients in the ICU, and the percentage of patients in the ICU who are intubed, in order to track whether these measures change through time as treatment protocols change.

Massachusetts Hospitalization Statistics
7 Day Trailing Averages
September 10, 2020
Hospitalization Statistic   Current 7 Days Ago 4 Weeks Ago
Covid Patients Hospitalized   330 309 392
Covid Patients in ICU   53 59 65
Covid Patients Intubed   23 26 29
7-Day Trailing Average New Confirmed Patients 21 19 20
 Percent ICU / Hospitalized   16% 19% 16%
 Percent Intubated / ICU   43% 45% 45%


There appears to be a small dip in the number of reported cases. It’s likely this is an artifact of the Labor Day holiday, as the number of new cases reported today (including 40 new suspected cases) was over 400. The number of new individuals tested did decline over the weekend, so that may be the main driver of the reduced case numbers, as positivity rates are up somewhat.

One technical note: going forward there will be small differences in the case numbers I report, and those reported by data aggregators. This is because the state continues to change the number of suspected cases of Covid historically. For example, on September 9, the state reported 182 confirmed cases of Covid, and no suspected cases, yet reduced the cumulative number of suspected cases by one. Since there is no information on when this suspected case occurred, I treat this as a day in which there were 182 suspected and confirmed cases. In contrast the data aggregators such as reported 181 confirmed and suspected cases yesterday. Not a big deal, at least given the current low number of revisions, but something to point out.

Massachusetts Reported Case and Death Statistics
7 Day  Trailing Average
September 10, 2020
Statistic   Current 7 Days Ago 4 Weeks Ago
Total Deaths   13 14 14
Deaths in Long-Term Facilities   8 7 11
Percent from Long-Term Care   60% 55% 81%
Total Cases Including Suspected   287 353 364

4 replies on “Massachusetts Data Update September 10, 2020”

Thank you for this! I’ve been waiting for your update. It’s making me crazy that the state is reporting .8% when it is in fact 2%. I know you’ve answered this before, but could you explain again why the discrepancy? Thank you so much in advance.

Sure. The difference is in whether the positivity rate is determined by considering tests or by considering individuals. The most common method is to consider individuals, not tests. In Massachusetts, about two-thirds of all tests are done for people who have been tested before, not individuals newly tested. Those repeat testers (these days highly likely to be students) have a very low positive rate, compared to the newly tested. My second blog post, “Calculating Covid-19 Positivity Rates” in the August archives, goes into this in more details.

I consider using individuals, not tests, to be a more accurate indication of how widespread Covid is. And Johns Hopkins, in their reporting, also considers suspected cases, which makes the positivity rate even higher (2.1% today, averaged over the past 7 days).

Thanks for clarifying the key metrics. I have always questioned the demographics of the new deaths and you have clarified what I was thinking. This information is very helpful.

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