Approval-Based Committee Voting in Practice: A Case Study of (Over-)Representation in the Polkadot Blockchain

TL;DR

This paper presents a large-scale analysis of approval-based committee elections on the Polkadot blockchain, examining overrepresentation and security implications of voting outcomes and design choices.

Contribution

It provides the first comprehensive real-world data analysis of approval-based elections in blockchain, focusing on overrepresentation and security-related measures.

Findings

Identification of overrepresentation patterns in Polkadot elections

Impact of committee size on overrepresentation and security

Comparison of standard proportionality and overrepresentation measures

Abstract

We provide the first large-scale data collection of real-world approval-based committee elections. These elections have been conducted on the Polkadot blockchain as part of their Nominated Proof-of-Stake mechanism and contain around one thousand candidates and tens of thousands of (weighted) voters each. We conduct an in-depth study of application-relevant questions, including a quantitative and qualitative analysis of the outcomes returned by different voting rules. Besides considering proportionality measures that are standard in the multiwinner voting literature, we pay particular attention to less-studied measures of overrepresentation, as these are closely related to the security of the Polkadot network. We also analyze how different design decisions such as the committee size affect the examined measures.