Leximax Approximations and Representative Cohort Selection

TL;DR

This paper introduces new approximate leximax solution concepts for selecting representative cohorts, providing efficient algorithms for linear utilities and analyzing computational hardness for integer solutions.

Contribution

It proposes novel approximate leximax notions, relates them to feasible algorithms, and proves NP-hardness for integer solutions in cohort selection.

Findings

Efficient polynomial-time algorithm for leximax distribution with linear utilities.

New approximate leximax notions with semantic interpretation.

NP-hardness of integer leximax cohort selection.

Abstract

Finding a representative cohort from a broad pool of candidates is a goal that arises in many contexts such as choosing governing committees and consumer panels. While there are many ways to define the degree to which a cohort represents a population, a very appealing solution concept is lexicographic maximality (leximax) which offers a natural (pareto-optimal like) interpretation that the utility of no population can be increased without decreasing the utility of a population that is already worse off. However, finding a leximax solution can be highly dependent on small variations in the utility of certain groups. In this work, we explore new notions of approximate leximax solutions with three distinct motivations: better algorithmic efficiency, exploiting significant utility improvements, and robustness to noise. Among other definitional contributions, we give a new notion of an approximate leximax that satisfies a similarly appealing semantic interpretation and relate it to algorithmically-feasible approximate leximax notions. When group utilities are linear over cohort candidates, we give an efficient polynomial-time algorithm for finding a leximax distribution over cohort candidates in the exact as well as in the approximate setting. Furthermore, we show that finding an integer solution to leximax cohort selection with linear utilities is NP-Hard.