Limitations — WP37 (audit version, 2026-11-01)
This file is the auditor's list; the manuscript's §9 is derived from it. Each item states the limitation, its consequence for the estimands, and whether the prospective design removes it.
| # | Limitation | Consequence | Removable by prospective design? |
|---|---|---|---|
| L1 | Posted (catalogue/circular) prices, no transactions, quantities or expenditure weights | No welfare statement; indices are unweighted (Jevons/Dutot/Carli), not CPIs; basket savings are posted-price upper bounds | No (would require scanner or receipt data) |
| L2 | 11 complete weeks (13 Aug – 22 Oct 2026) | H3 registered minimum 26 weeks not met → exploratory; no seasonality; recurrence right-censored; StatCan overlap 2 months | Yes (duration) |
| L3 | No store identifiers; storefronts answered anonymous sessions (store-mixture); circulars for one postal code | H4 geography untestable; Model E travel costs illustrative; QGPAI component 5 empty; within-banner dispersion bounded but store-unidentified | Yes (store pinning, multiple postal codes) |
| L4 | Regular price, on-sale flag, stock, size label stored as current state only | Promotion state inferred (10 % rule); shrinkflation unobservable; stock unusable | Yes (log three extra fields) |
| L5 | Matching: UPC only for Metro/Super C; tier B precision 0.932 on UPC truth (hidden variants); operator-reviewed labels, no independent coder yet | ~7 % of tier-B pairs may compare packaging variants; validation statistics not inter-rater | Partly (PI adjudication; GTIN exposure from more feeds) |
| L6 | 93 % of matched group-weeks are within-company (Metro/Super C; Maxi/Provigo/Club Entrepôt) | "Competition" evidence is mostly format segmentation; cross-company sample 2 103 group-weeks | Partly (more cross-chain UPC coverage) |
| L7 | Assortment coverage uneven: four Shopify feeds = 52 % of active listings; chains read on selected aisles | Market-level statistics not expenditure-representative; banner-level results fine | Yes (connector scope) |
| L8 | Promotion rule edge effects: trailing 8-week mode on an 11-week panel; first weeks promotion-poor | QGPAI promo component NaN in week 1; 42 % of low-price episodes are regular-price resets (A-003) | Yes (duration) |
| L9 | Model C: no exogenous variation; cross-company lead placebo fails | No causal spillover claim; same-company lags interpretive only | Only with a natural experiment |
| L10 | Three post-registration amendments (A-001 basket block; A-002 unit-price screen; A-003 episode classes) | Documented; preregistered basket rule gave 7 items (result in decisions log) | — |
| L11 | Clustering: 14 banners in matched storefront sample; two-way SEs unreliable; no wild-cluster bootstrap | Banner-effect SEs indicative | Partly |
| L12 | "Autres" residual category = 19 % of active listings | Category heterogeneity understated | Yes (taxonomy) |
| L13 | LLM used as second annotator (claude-opus-5-5, 1.58 USD total over four runs); not independent of operator review | Validation labels are a reviewed single-source label | PI adjudication |
| L14 | Company attributions for affiliated banners from registry text | Affects same-/cross-company split only | Corporate source check |