Perludem, together with International IDEA, has prepared the presentation Simulation of a Mixed Electoral System for Indonesia as a technical study addressing one fundamental question: had the 2024 DPR election been held under the rules of a mixed electoral system, what seat composition would it have produced? Holding voters’ ballots exactly as cast in 2024, the simulation traces the entire chain of converting votes into seats, from data, formulas, and the reallocation of seats across provinces to the drawing of electoral districts, under a range of system designs, principally the parallel system and Mixed-Member Proportional (MMP), with List Proportional Representation (List PR) serving as a benchmark.
The study covers 14 scenario cells (eight MMP variants, four parallel, and two List PR benchmarks), computed on the 2020 BPS census population, the official results of the 2024 DPR election, and a 580-seat DPR. The drawing of single-member districts, something never before seen in Indonesia’s electoral history, was built from scratch using the Electoral Redistricting App (ERA), while the conversion of votes into seats relies on the LR-Hare and Sainte-Laguë formulas. The presentation sets out the full methodology, including the boundaries it deliberately did not simulate, so that the findings can be read accurately.
Among the key findings: the tier at which party lists are drawn (national or provincial) shapes the outcome more than the district to list seat ratio; provincial lists generate overhang seats that inflate the size of the DPR; the parallel system departs furthest from proportionality; and the 4 percent parliamentary threshold is the largest source of disproportionality, leaving 11.4 percent of valid 2024 votes unconverted into seats. It bears emphasis that the simulation is not a projection of the 2029 election and does not recommend any particular system. The figures shown are the product of converting rules, offered as a technical basis for weighing the consequences of each design choice before the rules are finalized.
Compiled by: Adhy Amman, Andrew Ellis, Heroik M Pratama, and Iqbal Kholidin.
