As COVID-19 cases, hospitalizations and deaths continue to rise in Alberta, there is another number Albertans should be thinking about: the R-value.

The R-value is essentially the number of people infected by each infected person. It's known as the reproduction number, R-number, or simply as "R."

Last week, as Premier Jason Kenney announced new restrictions on gatherings and businesses, he also revealed that the R-value will be the key metric in determining whether those restrictions will be lifted on Dec. 18.

Kenney said then he would evaluate the restrictions on Dec. 15, and the province would need to have an R-value below 1.0 in order to lift the restrictions. Ideally, he said, the province would have a R-value of 0.8. 

"That's the minimum metric goal that we must achieve by December the 15th," he said. "We must see the rate of transmission move below one. If we start to move it below one, then we know we have begun effectively to bend the curve."

An R-value of one means with each person with the illness only infects one other person. That would mean the number of infected people would be fairly consistent. Any number above one means case numbers will grow.

• Why the R is a key COVID-19 metric to watch 

On Tuesday, Dr. Deena Hinshaw, the province's chief medical officer of health, said it had been "at least a month" since Alberta last saw an R-value of one. The metric is useful in understanding whether the restrictions were working, she said, though the impact of the measures announced last week wouldn't be seen until later this week at the earliest.

"As I said, that is one of the most important metrics right now," she said. "Because it does help us understand whether our actions are decreasing the curve enough to actually have that reduction in number of cases. Because that is the only way that we are going to be able to alleviate the pressure on the health-care system."

Hinshaw said that even if Alberta got to one and was able to hold case numbers steady, "We would still see the current impact and pressure on the health-care system."

Alberta Health spokesperson Tom McMillan told CBC last week the provincial R-value as of Nov. 23 was 1.12. Though CBC asked for the information several times over numerous days, Alberta Health did not provide a more recent R-value for the province.

On Wednesday, Kenney said cabinet will discuss the possibility of publicly releasing the R-value, as well other metrics, at its next meeting. He said the provincial positivity rate is also and important metric that is publicly available.

That rate was 9.2 per cent on Wednesday, the highest level since the pandemic began.

Craig Jenne, associate professor in the department of microbiology, immunology and infectious diseases at the University of Calgary, said the R-value is an important marker but has limitations. 

"Although we often see an R-value, for example, for the province of Alberta, it is likely not uniform across the province," said Jenne. "Just because Alberta may have an R-value of a certain amount, it doesn't mean all communities have that same R-value. Or more importantly, not all areas, even within a single community, would have the same R-value. 

"It's a global measurement, but it can be over-interpreted and it may not reflect sort of what's happening at the ground level within specific environments in the province."