Abstract
Party-list proportional representation methods aim to allocate seats proportionally to the votes cast for each party. In general, exact proportionality is not possible as it would require a fractional allocation of seats. Therefore several methods have been devised to compute seat allocations that differ in the way they try to achieve proportionality. Examples of such methods include the d’Hondt and Sainte-Laguë methods that allocate seats according to fractional values. These methods are used in many countries. Numerically, these fractions appear harmless, however they are not. Computers do not work with infinite precision floating point numbers, implementations tend to round the fractions to several digits, which can, with a certain probability, lead to incorrect seat allocations.
C. Schürmann—This paper was made possible by grant NPRP 097-988-1-178, Automated verification of properties of concurrent, distributed and parallel specifications with applications to computer security, from the Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility of the author.
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Acknowledgements
The author would like to thank the Danish Ministry for Economic Affairs and the Interior and Statistics Denmark for their support and cooperation. The author would also like to thank Prof. Jørgen Elklit for comments on earlier drafts of this paper.
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Schürmann, C. (2018). Rounding Considered Harmful. In: Krimmer, R., et al. Electronic Voting. E-Vote-ID 2018. Lecture Notes in Computer Science(), vol 11143. Springer, Cham. https://doi.org/10.1007/978-3-030-00419-4_13
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DOI: https://doi.org/10.1007/978-3-030-00419-4_13
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