Change Management Policy
A reference series is only useful if the reader knows when and how the measurement underneath it can change. This policy governs every change to the Methodology.
01 Versioning
Every published row carries a methodology version. A change to collection, aggregation, panel rules, or series definitions increments the version; history restated under a new version is stamped with it row by row, so any historical value can be traced to the methodology that produced it.
02 Classification
Non-material changes — defect fixes, source additions or exits under the existing panel rules, new series on existing grammar — are applied and noted in the data repository's change log.
Material changes — a material change is one that, applied to the trailing history, would move a headline series' 30-day average by more than 10%. Material changes are announced on the site before taking effect where practicable, and are run as parallel (shadow) series alongside the incumbent before promotion whenever the change permits it.
Announcements are made in the Methodology Change Log, each with its effective date, the anticipated effect on the published series (quantified where estimable, stated as none expected otherwise), and a comment window. At the effective fixing, the realized effect — the with/without decomposition — is appended alongside the anticipated figure, so the log carries the record of what was estimated and what occurred. Changes below the material threshold that touch panel membership or series composition follow the same practice.
Series breaks — a change that redefines what a series measures (its universe, segment definition, or price basis) is not made in place: the old series ends and a new identifier begins. In-place history is never silently redefined.
03 Restatements
When a defect or a material change requires it, history is restated: republished in full under the current methodology version. Restated snapshots replace prior ones at the published locations; prior versions remain retrievable through the data repository's history. Restatements are disclosed in the change log with the reason and the affected range.
04 Panel changes
The source panel is versioned. New sources enter only through a panel version change; a source that stops publishing carries forward at its last-good price for at most seven days and then exits its cells. A source's exit or entry is never applied retroactively except through a disclosed restatement.