1% ============================================================================2% UQO Working Paper Template — Economics / Finance3% ============================================================================4\documentclass[12pt,letterpaper]{article}56% --- Encoding & Language ---7\usepackage[utf8]{inputenc}8\usepackage[T1]{fontenc}9\usepackage[english]{babel}1011% --- Page Layout ---12\usepackage[13 letterpaper,14 top=1in,15 bottom=1in,16 left=1in,17 right=1in18]{geometry}1920% --- Typography ---21\usepackage{mathptmx} % Times-like font (text + math)22\usepackage{microtype} % Improved typographic refinements23\usepackage{setspace}24\onehalfspacing % 1.5 line spacing2526% --- Math ---27\usepackage{amsmath,amssymb,amsthm}2829% --- Tables ---30\usepackage{booktabs}31\usepackage{tabularx}32\usepackage{multirow}33\usepackage{threeparttable}34\usepackage{siunitx}35\sisetup{36 input-symbols = {()},37 table-format = -1.3,38 parse-numbers = false39}4041% --- Figures ---42\usepackage{graphicx}43\usepackage{subcaption}44\usepackage{float}45\usepackage{adjustbox}4647% --- Colors & Links ---48\usepackage[dvipsnames]{xcolor}49\usepackage[50 colorlinks = true,51 linkcolor = NavyBlue,52 citecolor = NavyBlue,53 urlcolor = NavyBlue,54 breaklinks = true55]{hyperref}5657% --- Bibliography ---58\usepackage[authoryear,round,semicolon]{natbib}59\bibliographystyle{aer}6061% --- Captions ---62\usepackage[63 font = small,64 labelfont = bf,65 labelsep = period,66 justification = justified,67 singlelinecheck = false68]{caption}6970% --- Headers & Footers ---71\usepackage{fancyhdr}72\pagestyle{fancy}73\fancyhf{}74\renewcommand{\headrulewidth}{0pt}75\fancyfoot[C]{\thepage}7677% --- Section Formatting ---78\usepackage{titlesec}79\titleformat{\section}{\large\bfseries}{\thesection.}{0.5em}{}80\titleformat{\subsection}{\normalsize\bfseries}{\thesubsection.}{0.5em}{}81\titleformat{\subsubsection}{\normalsize\itshape}{\thesubsubsection.}{0.5em}{}8283% --- Appendix Support ---84\usepackage[toc,page]{appendix}8586% --- Misc ---87\usepackage{enumitem}88\setlist{nosep,leftmargin=*}8990% ============================================================================91% METADATA — Edit these fields for each working paper92% ============================================================================93\newcommand{\WPnumber}{37}94\newcommand{\WPtitle}{The Hidden Architecture of Grocery Prices: Promotions, Retail Competition, and the Cost of Living in Quebec}95\newcommand{\WPsubtitle}{Evidence from 300{,}613 posted-price events across 54 Quebec grocery feeds, August--November 2026}96\newcommand{\WPdate}{November 2026}97\newcommand{\WPversion}{1.0}98\newcommand{\WPabstract}{%99Grocery prices are not a single inflation process. Using a read-only research copy of Food-Ka, a Quebec grocery price aggregator, we assemble an auditable panel of 124{,}579 listings from 54 active source feeds (26 retail companies, two channels: online storefronts and weekly circulars) observed every seven hours between 12 August and 1 November 2026 (300{,}613 logged price events, 723{,}140 listing-weeks). We first document a measurement finding that matters for any study of scraped grocery prices: storefronts that answer anonymous sessions with store-specific prices generate intra-day oscillation among three to five price levels, so that sub-weekly ``volatility'' in such feeds is a mixture over unidentified stores, not repricing. We then build a calibrated cross-banner matching procedure (exact UPC within Metro Inc.; brand, package and token-identical names elsewhere), validated against 4{,}413 UPC-identified pairs (precision 0.91, recall 0.98) and a 240-pair reviewed sample, which yields 5{,}909 cross-banner groups. On identical products in the same week, the median max--min log price gap across banners is 0.154 (79\% of group-weeks exceed 5\%), banner-pair gaps are persistent (AR(1) 0.66 against a 0.00 permutation placebo), and banner fixed effects range from $-0.20$ (Walmart, Giant Tiger, Maxi) to $+0.12$ (specialty shops) relative to Metro. Inferred promotions cover 4.6\% of storefront listing-weeks with a median depth of 22\%; half of all weekly price changes are promotion entries or exits, doubling measured volatility (ratio 1.92, CI 1.84--2.02). Temporary sales return exactly to their pre-sale reference (mean change $-0.0003$ log points), i.e. we find no reference-price drift after promotions in this window; a pre-sale price elevation is concentrated in store-mixture feeds and shrinks to about two log points in single-store shops. Lead--lag price associations between rivals are small and fail a lead placebo for cross-company pairs, so no causal response is claimed. Over eleven weeks, matched-model and naive indices agree within one percentage point for storefronts, but naive averages are off by 10--30 points for banners with assortment turnover. A fixed-basket mixed-integer program shows that unconstrained cheapest-banner shopping saves 15\% relative to the best single banner, 85\% of which is captured with two banners; store geography and travel costs are unobserved and treated as explicit limitations. We publish the five-component Quebec Grocery Price and Affordability Index with uncertainty bands and a prospective collection plan, and we report null and failed tests alongside positive ones.%100}101\newcommand{\WPkeywords}{grocery prices; price dispersion; promotions; high--low pricing; web-scraped prices; price indices; record linkage; retail competition; Quebec}102\newcommand{\WPjel}{D22, D40, E31, L11, L81, C81}103104% --- Author ---105\newcommand{\WPauthor}{Simon-Pierre Boucher}106\newcommand{\WPaffiliation}{%107 Département des sciences administratives\\108 Université du Québec en Outaouais%109}110\newcommand{\WPemail}{simon-pierre.boucher@uqo.ca}111\newcommand{\WPaddress}{%112 Gatineau -- Pavillon Alexandre-Taché\\113 283, boulevard Alexandre-Taché\\114 Gatineau, Québec, Canada J9A 1L8%115}116117% ============================================================================118% DOCUMENT119% ============================================================================120\begin{document}121122% --- Title Page ---123\input{sections/titlepage}124125% --- Main Body ---126\input{sections/introduction}127\input{sections/literature}128\input{sections/institutional}129\input{sections/data}130\input{sections/theory}131\input{sections/methods}132\input{sections/results}133\input{sections/robustness}134\input{sections/policy}135\input{sections/limitations}136\input{sections/conclusion}137\input{sections/reproducibility}138139% --- References ---140\newpage141\bibliography{references}142143% --- Appendix ---144\input{appendix/appendix}145146\end{document}147