Ex-Post Evaluation of Mean-Variance Cartel Filters

Abstract

This study provides an ex-post evaluation of selected filters to find cartels. We evaluate whether filters incurred in type I errors, i.e., failing to recognize the presence of a cartel. We use seven cartel cases in the retail fuel sector in Brazil, for which detailed local price and gross retail margins are available. Cartel cases provided 14 fuel-location events. The evaluated methods include GARCH-based and structural break methods from the international literature and three filters associated with Brazilian antitrust and regulation authorities (ANP, SBDC, and local correlation). All methods are based on an analytical framework which considers cartels as periods of higher average prices (margins) and lower price (margin) variance. Our results indicate that our filters failed to correctly signal most fuel-location cartel events, even using endogenous model-based price changes dates. The problems filters show of detecting actual cartels may be due to difficulties dating cartels or the possibly inappropriate use of price mean-variance markers to evaluate cartel behavior.