While Alberta's new COVID stats page can be confusing, Dr. Craig Jenne explains some key numbers and what they mean

Alberta's new respiratory virus dashboard provides weekly updates on the spread of COVID-19 in the province, but making sense of the numbers can be a challenge — and it's particularly difficult to figure out how many people have died.

For example, Albertans who visited the dashboard in mid-November were greeted by a front-page "highlights" package informing them there had been two deaths from COVID-19 during the past reporting week.

That was technically true.

Equally true — but less obvious — was the fact that there were actually 18 more deaths in that week's report, compared with the report from the week before. How can both numbers be correct?

Here's what's going on.

Of the 18 additional deaths included in that week's report, just two occurred during the reporting week of Nov. 5 to 11. That's pretty typical, given how long it takes for COVID deaths to be recorded and included in the provincial data. The process can often takes weeks, sometimes more than a month. This reporting lag means many of the deaths in each weekly report actually happened in prior weeks.

Nowhere on the site, however, was it made explicit that 18 more people had died, in total, including those from prior weeks.

To figure that out, a visitor would have to recall the total number of deaths cited in the previous week's report, then subtract that from the total number of deaths in the most recent report. The province's decision to present the data in this way can create a misleading picture, says Craig Jenne, a professor in the department of microbiology, immunology and infectious diseases at the University of Calgary.

"We see this number that seems really small, and it maybe leads to a false sense of security," he said.

"We've seen, almost without variance, numbers going up in subsequent weeks."

To illustrate, the animated chart below shows how the weekly death totals retroactively grew in subsequent reports from September to November.

Animated image of COVID-19 deaths included in Alberta's weekly reports from September to November, and when the deaths actually happened. (Robson Fletcher/CBC)

To help Albertans make more sense of the numbers, CBC News has developed an automated system to extract data from the provincial dashboard and present the information in a different way.

You can find that in the series of charts and tables below.

The same data, presented differently

First up, a different version of the "highlights" — one that reflects all the newly reported deaths from week to week, and other severe outcomes.

The table below summarizes how many more deaths and hospital admissions (both non-ICU and ICU) there were in the province's most recent weekly report, compared to the report from the week before.

The next chart provides more detail on when deaths happened. Each column in the chart below represents the number of COVID-19 deaths in a given week of the current respiratory-virus season. Bear in mind the reporting lag, however: recent weeks will typically represent an undercount of the actual number of deaths. The numbers will often be revised upward, as more deaths from a given week are reported in the future.

Similarly, the next chart shows when people were hospitalized.

Each bar shows the number of people admitted to hospital in a given week. Admissions to intensive care units (ICU) are shown in red and non-ICU admissions are depicted in yellow. Only people who have a lab-confirmed case of COVID-19 and were admitted to hospital because of COVID-19 are included in this public-facing data.

Alberta Health Services also tracks the total number of COVID-positive patients in hospital, including those who were admitted for other reasons, but it does not report that publicly. CBC News has obtained these internal reports in the past and the numbers are higher that those in the public-facing data.

With the public-facing data, there can also be a reporting lag of a week or more.

"Hospital and ICU admission data can have reporting delays," Alberta Health explains in its data notes. "Data for the previous week may be incomplete and should be interpreted with caution as updates may occur in the following weeks as case report forms are submitted by AHS."

The next data visualization breaks down severe outcomes by age. For each age range in the table below, you will find the total number of hospitalizations, ICU admissions and deaths in the current respiratory-virus season. You'll also find the population-adjusted rate (per 100,000 people) for each age range. 

As someone who studies infectious disease, Jenne says it's "frustrating" to see how long it now takes for COVID-19 data to make its way to the public.

"When those numbers are not kept up in real time and instead are revised over the course of weeks or months, it's not equipping the public with the information they need to to make the best informed decisions," Jenne said.

CBC News reached out to Alberta Health about the way data is presented on the dashboard but has yet to receive a reply.