Interpretation of excess mortality depends critically on baseline choice. This commentary examines the recent debate on all-cause mortality in Norway in 2024 and argues that it reflects a conflation of two distinct purposes: real-time surveillance using updated baselines and assessment of whether mortality has returned to the pre-pandemic improvement trajectory. These correspond to different estimands and are not interchangeable. Baseline redefinition has predictable inferential and communicative consequences, particularly in public-facing outputs. I argue that the main risk lies not in modeling choices themselves, but in insufficiently explicit communication. Transparent reporting with clearly labeled baselines is essential to avoid interpretive drift.
Jörn Klein (Sun,) studied this question.