Findings
How competitive is each NBA season?
Descriptive only. Win-share concentration differs across the covered NBA seasons, and the ledger reports how balanced each one was. It does not say why.
no packet verdict (descriptive exhibit)n = 3 seasons, 3,611 gamesno intervaldate not publishedleague_parity_index.jsondate not publishedvalidation_pendingFindings are exploratory unless a pre-registration file, date and hash are shown on the page.
How it was tested
- Gate: descriptive: season-level concentration index with declared game floors
- Corpora: NBA game results by season
- Folds: none
Replication
single corpus
Inspector
No inspector page for this finding.
team-game points = sum of a team's players' pts within one game_id. Gini of per-team win counts (wins/total-wins sum to 1); 0 = balanced, (N-1)/N = one team hoards all
Win-share Gini rose from 0.177 in 2023-24 to 0.2004 in 2025-26 -- across the three seasons on disk, the league looks more top-heavy, not more balanced. Two of those three seasons are partial vs. a full 1230-game season, so read this as a small, honest description, not a trend.
| Season | Games | Teams | Win-share Gini | Win% stdev | Mean abs margin | % close (≤5) |
|---|---|---|---|---|---|---|
| 2023-24 | 1230 | 30 | 0.177 | 0.1636 | 12.58 | 23.3 |
| 2024-25partial season | 1225 | 30 | 0.1798 | 0.1629 | 12.71 | 25.2 |
| 2025-26partial season | 1156 | 30 | 0.2004 | 0.1667 | 13.03 | 25.5 |
Scroll horizontally for all columns.
Methodology and confounds
- only game_ids with exactly 2 distinct teams; higher score wins (ties excluded from margins)
- Herfindahl of win shares; balanced floor = 1/N; normalized = (HHI-1/N)/(1-1/N)
- std of team win percentage -- games-normalized companion (robust to unequal game counts)
- mean/std of absolute final margin + pct of games decided by <= 5 points
- Games floor: 200 per season -- season below the floor is flagged meets_games_floor=false and excluded from the Lorenz chart. Full-season reference = 1230 games.
- NOT a prediction of any future season's parity (describes seasons already played)
- NOT reg-season-only (pooled with any playoff games in the parquet, which inflate win concentration)
- NOT strength-of-schedule adjusted (opponent-raw win counts)
- Results report season-level concentration measures with the stated games floor.
Limitations
- Sample and independence: one value per season, so the season-to-season comparison rests on very few points.
- Scope: the covered NBA seasons; an in-progress season is partial against the declared floor.
- Does not establish why parity moved, or that the trend continues.
Verdict history
- : current: no packet verdict (descriptive exhibit)