Do not compare opening-day and final-day win rates as if they came from the same population. Withdrawals change who remains, records affect the meaning of later matchups, and defaults change the denominator. Identify the wrestlers, opponents and result types before attributing a difference to the day itself.
The Japan Sumo Association’s daily results are bout-level primary evidence. Placing fifteen pages in one spreadsheet, however, does not automatically create a fair time series. The final-day roster is not simply the opening-day roster observed fourteen days later.
The population changes during the tournament
A withdrawal changes both the number and composition of wrestlers available later. A return, a full absence and a lower-division no-bout day are different states. A blank must not become a win or a loss. Store contested bouts, fusen decisions and no scheduled bout separately.
Later matchups can also reflect rank, record and the evolving competitive situation. A difference labelled “final-day pressure” may partly be a difference in opponent composition. Retain each opponent, banzuke position and record known before the bout. The official result records what happened; it does not isolate fatigue, motivation or pressure.
Survivor selection can reverse the question
Selecting only wrestlers who completed all fifteen days removes paths that ended in withdrawal. That can answer a question about full-tournament participants, but not about the opening-day cohort. Publish those two groups separately.
For a claim such as “this wrestler is strong on senshuraku,” show two denominators: final days actually reached and all tournaments entered at the start. Predefine the interval, division, rank range and minimum number of tournaments. Do not add an interesting wrestler only after seeing the result.
What every day-by-day table needs
- contested bouts, defaults and no-bout or absence states by day;
- division, date range, rank scope and treatment of returns;
- whether the denominator is wrestlers or bouts;
- retrieval time for provisional data and a post-tournament reconciliation date.
Small differences should remain counts and uncertainty, not a dramatic league table. Fifteen equal column widths can conceal fifteen unequal samples.
Separate an observed gap from an imagined cause
The defensible question is whether recorded outcomes differ by day within one declared division, interval and cohort. Fatigue or pressure may be hypotheses, but the scorecard does not measure them directly. A gap that disappears after opponent adjustment, reverses between completers and the opening-day cohort, or depends on one tournament is counterevidence to a simple day story.
In-progress tables remain provisional until the official scorecard and all fifteen result pages are reconciled after senshuraku. If a later absence mark or default is corrected, preserve the former value and link every repaired chart and sentence. “No stable difference” is a result worth publishing, not a failed search for drama.
Turn the warning into a viewing cue
Choose one day and inspect the matchup list before its aggregate win rate. Notice two wrestlers with similar records and ask what each needs from the first step. The data then becomes more than a calendar of percentages: it becomes an invitation to see how the tournament’s changing shape reaches the dohyo.
Sources
- Japan Sumo Association daily bouts/results, tournament scorecard and absence information (checked 3 September 2026).
Source links used for verification
Each link was used for the corresponding claim in this article; inclusion is not a blanket endorsement of the whole page.
Article verified:
- Japan Sumo Association daily bouts and resultsPrimary source (as checked for this article)
- Japan Sumo Association tournament scorecardPrimary source (as checked for this article)
- Japan Sumo Association absence informationPrimary source (as checked for this article)