Non-uniform Bid-scaling and Equilibria for Different Auctions: An Empirical Study

TL;DR

This empirical study compares auction formats like FPA, GSP, and VCG under uniform and non-uniform bid-scaling, revealing their relative performance and the impact of bid-scaling strategies on welfare and profit.

Contribution

It provides the first empirical analysis of how non-uniform bid-scaling affects different auction formats in autobidding environments.

Findings

FPA outperforms GSP and VCG in welfare and profit.

Non-uniform bid-scaling reduces welfare in FPA and GSP.

VCG's performance is unaffected by bid-scaling levels.

Abstract

In recent years, the growing adoption of autobidding has motivated the study of auction design with value-maximizing auto-bidders. It is known that under mild assumptions, uniform bid-scaling is an optimal bidding strategy in truthful auctions, e.g., Vickrey-Clarke-Groves auction (VCG), and the price of anarchy for VCG is $2$. However, for other auction formats like First-Price Auction (FPA) and Generalized Second-Price auction (GSP), uniform bid-scaling may not be an optimal bidding strategy, and bidders have incentives to deviate to adopt strategies with non-uniform bid-scaling. Moreover, FPA can achieve optimal welfare if restricted to uniform bid-scaling, while its price of anarchy becomes $2$ when non-uniform bid-scaling strategies are allowed. All these price of anarchy results have been focused on welfare approximation in the worst-case scenarios. To complement theoretical understandings, we empirically study how different auction formats (FPA, GSP, VCG) with different levels of non-uniform bid-scaling perform in an autobidding world with a synthetic dataset for auctions. Our empirical findings include: * For both uniform bid-scaling and non-uniform bid-scaling, FPA is better than GSP and GSP is better than VCG in terms of both welfare and profit; * A higher level of non-uniform bid-scaling leads to lower welfare performance in both FPA and GSP, while different levels of non-uniform bid-scaling have no effect in VCG. Our methodology of synthetic data generation may be of independent interest.