For a number of reasons, as time goes on vaccines become less effective. So how do researchers calculate how well vaccines are working?

Using a robust statistical model, researchers estimate that coronavirus vaccines had prevented 140,000 deaths by May 9, 2021.

The vaccine rollout is underway, but what happens if there is a supply disruption? Would it be feasible to change strategy and give more people a first dose? An expert analyzes the data.

Whether you are predicting the outcome of an election or studying how effective a new drug is, there will always be some uncertainty. A margin of error is how statisticians measure that uncertainty.