Exposure misclassification: an “immortal time” bias in observational studies of training load and injury
Bibliographic record
Abstract
BACKGROUND: Several observational studies of the relationship between training load and injury have found increased risks of injury at low loads. These associations are expected because load is often assessed at the end of the injury follow-up period. As such, athletes who get injured earlier in the follow-up period will have systematically lower loads than athletes who get injured later in the follow-up period. OBJECTIVE: In this commentary, we identify this problem as a type of exposure misclassification occurring from the misalignment of exposure measurement and start of follow-up. This methodological issue has previously been recognized in other areas of epidemiology as "immortal time bias." RESULTS AND CONCLUSION: Similar to immortal time bias, exposure misclassification bias can be prevented by aligning the measurement of load with the start of follow-up for injury.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.147 | 0.309 |
| Meta-epidemiology (narrow) | 0.001 | 0.002 |
| Meta-epidemiology (broad) | 0.002 | 0.004 |
| Bibliometrics | 0.003 | 0.004 |
| Science and technology studies | 0.002 | 0.004 |
| Scholarly communication | 0.003 | 0.005 |
| Open science | 0.005 | 0.004 |
| Research integrity | 0.004 | 0.004 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".