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The potential of iterative voting to solve the separability problem in referendum elections

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Abstract

In referendum elections, voters are often required to register simultaneous votes on multiple proposals. The separability problem occurs when a voter’s preferred outcome on one proposal depends on the outcomes of other proposals. This type of interdependence can lead to unsatisfactory or even paradoxical election outcomes, such as a winning outcome that is the last choice of every voter. Here we propose an iterative voting scheme that allows voters to revise their voting strategies based on the outcomes of previous iterations. Using a robust computer simulation, we investigate the potential of this approach to solve the separability problem.

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Notes

  1. We thank the anonymous referee for raising this point.

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Acknowledgments

This work was partially supported by National Science Foundation Grant DMS-1003993, which funds a Research Experience for Undergraduates program at Grand Valley State University.

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Correspondence to Jonathan K. Hodge.

Appendix: profile details

Appendix: profile details

Profile 1

Every voter ranks the ASI-optimal outcome (101) \(4^\mathrm{th}\).

$$\begin{aligned} \left( \begin{array}{ccc} 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 0 \end{array} \right) ~~~\left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 0 \end{array} \right) ~~~\left( \begin{array}{ccc} 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 1 \end{array} \right) \end{aligned}$$

Profile 2

Simultaneous voting elects the worst possible outcome (111); 2 variations.

$$\begin{aligned}&Variation 1: \left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \end{array} \right) \\&Variation 2: \left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \end{array} \right) \end{aligned}$$

Profile 3

The ASI-optimal outcome (011) results from every voter voting their \(3^\text{ rd }\) choice; the \(2^\text{ nd }\) best outcome (010) results from every voter voting their \(2^\text{ nd }\) choice.

$$\begin{aligned} \left( \begin{array}{ccc} 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 1 \end{array} \right) \end{aligned}$$

Profile 4

There is a dominating block whose \(2^\text{ nd }\) choice is ASI-optimal (3:2 ratio); 2 variations.

$$\begin{aligned}&Variation 1: \left( \begin{array}{ccc} 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \end{array} \right) \\&Variation 2: \left( \begin{array}{ccc} 1 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \end{array} \right) \end{aligned}$$

Profile 5

All voters’ preferences are separable on the first two proposals; some are separable on other sets.

$$\begin{aligned} \left( \begin{array}{ccc} 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 1 \end{array} \right) \end{aligned}$$

Profile 6

There are multiple ASI-optimal outcomes; 2 variations.

$$\begin{aligned}&Variation 1: \left( \begin{array}{ccc} 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \end{array} \right) \\&Variation 2: \left( \begin{array}{ccc} 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \end{array} \right) \end{aligned}$$

Profile 7

The Condorcet winner (010) is ASI-optimal and elected by simultaneous voting (18:14:18 ratio); a Condorcet loser (100) is also present.

$$\begin{aligned} \left( \begin{array}{ccc} 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \end{array} \right) \end{aligned}$$

Profile 8

Two diametrically opposed voter blocks; 1 variation with a dominating block (2:3 ratio); 1 variation with equal numbers of voters in each block.

$$\begin{aligned}&\left( \begin{array}{ccc} 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \end{array} \right) \\&\left( \begin{array}{ccc} 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \end{array} \right) \end{aligned}$$

Profile 9

Three main blocks; the third block is divided into 6 sub-blocks, all of which agree on their first choice but differ on subsequent choices (17:17:3:3:3:3:3:3 ratio).

$$\begin{aligned}&\left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \end{array} \right) \\&\left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \end{array} \right) \end{aligned}$$

Profile 10

The three outcomes with the lowest ASIs (110, 101, 011) agree with the ASI-optimal outcome (111) on 2 of 3 proposals.

$$\begin{aligned} \left( \begin{array}{ccc} 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 1 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \end{array} \right) \end{aligned}$$

Profile 11

The ASI-optimal outcome (110) is the complement of the simultaneous voting outcome (001); 2 variations, each with 28:28:24:20 ratio.

$$\begin{aligned}&Variation 1: \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 0 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 0 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \end{array} \right) \\&Variation 2: \left( \begin{array}{ccc} 1 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 1 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 0 \end{array} \right) ~~\left( \begin{array}{ccc} 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 1 \\ 1 &{} 0 &{} 0 \\ 0 &{} 1 &{} 0 \end{array} \right) \end{aligned}$$

Profile 12

There is a dominating block whose first choice (111) is ASI-optimal and whose last choice (100, a Condorcet loser) is the first choice of all other voters (26:12:12 ratio).

$$\begin{aligned} \left( \begin{array}{ccc} 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 0 &{} 1 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 0 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 0 \\ 1 &{} 1 &{} 0 \\ 0 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 0 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \\ 1 &{} 1 &{} 1 \end{array} \right) \left( \begin{array}{ccc} 1 &{} 0 &{} 0 \\ 0 &{} 0 &{} 1 \\ 1 &{} 1 &{} 0 \\ 1 &{} 0 &{} 1 \\ 0 &{} 0 &{} 0 \\ 1 &{} 1 &{} 1 \\ 0 &{} 1 &{} 1 \\ 0 &{} 1 &{} 0 \end{array} \right) \end{aligned}$$

Profile 13

10 randomly generated blocks with equal numbers of voters.

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Bowman, C., Hodge, J.K. & Yu, A. The potential of iterative voting to solve the separability problem in referendum elections. Theory Decis 77, 111–124 (2014). https://doi.org/10.1007/s11238-013-9383-2

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