A figure which is designed to measure the degree of deviation from proportionality in the allocation of seats to parties or groupings which participated in the election. It is most commonly defined as the square root of the sum of the squares of the differences for each party or grouping between the percentage of votes received and the percentage of seats gained.
Understand more election terms clearly
Get one important election term explained each week, with authoritative sources, practical context and related definitions.
A figure which is designed to measure the degree of deviation from proportionality in the allocation of seats to parties or groupings which participated in the election. It is most commonly defined as the square root of the sum of the squares of the differences for each party or grouping between the percentage of votes received and the percentage of seats gained.
Cite this term
Election Security Glossary. (2026). Index Of Disproportionality. In Election Security Glossary. Retrieved August 20, 2026, from https://electionsecurityglossary.com/glossary/index-of-disproportionality
Sources
01
Single-source
Get the weekly election term
Receive one cited, source-backed election explanation in your inbox each week.