How early can the splits reveal how the race will finish?

Hold out the latest three observed calendar years (2024–2026). Fit every factor and the 10th–90th percentile ratio interval on earlier years only. Training cells need at least 100 records; missing trend cells fall back to the pace-band model, then the pooled training model. No future splits, finishing-time groups, identities or supplied ability fields enter a prediction.

Report median absolute error for all three methods, plus observed coverage and median width of the nominal 80% prediction interval and the 90th percentile absolute error. Model selection is fixed before examining these results. A runner may occur in training and test in different years; identities are not used. Results apply to complete eligible finishers and do not predict withdrawals.

Use complete, strictly increasing elapsed checkpoints at 3.11, 6.21, 9.32, 12.43, 15.53, 18.64, 21.75, 24.85 and 26.22 mi. Clock strings must parse as H:MM:SS or M:SS. No missing splits are interpolated.

Remove exact duplicate race records, ignoring database IDs, ingestion timestamps and source URLs. Retain finishes from 90 minutes to 12 hours with every section between 3.22 and 32.19 minutes/mi. These quality filters can exclude genuine unusual performances; the analysis describes this eligible cohort, not every entrant.

Full source records are available in public GitHub Releases. These chart tables require at least 100 eligible observations per cell for estimate reliability. Counts refer to finishes, linked pairs or event observations as specified in that answer.

These are observational results. Fitness changes, intentions, training, selection into the dataset and unmeasured conditions can explain differences. Outcome percentiles describe variation among performances, not confidence intervals or advice about the best strategy.

Apply the reviewed source-quality edition exclusions for this exact export after the timing checks. Known invalid split grids, incomplete ingestion, unreconciled HOLD editions and a selected top-finisher field do not contribute to the analyses or prior benchmarks. Report source exclusions separately; an already invalid timing row is not counted twice. Missing age or recorded gender alone does not exclude an otherwise eligible finish from the overall cohort. Other sparse editions are not declared incomplete merely from their size.

Marathons, years and recorded data. Chart samples may be smaller than the eligible analysis cohort.