Research

Experimental Economics (2025), 28(5):1085-1100 · Journal version · GitHub · Interactive experiment builder · Abstract · Citation

Large Language Models (LLMs) have the potential to profoundly transform and enrich experimental economic research. We propose a new software framework, “alter_ego”, which makes it easy to design experiments between LLMs and to integrate LLMs into oTree-based experiments with human subjects. Our toolkit is freely available at github.com/mrpg/ego. To illustrate, we run differently framed prisoner's dilemmas with interacting machines as well as with human-machine interaction. Framing effects in machine-only treatments are strong and similar to those expected from previous human-only experiments, yet less pronounced and qualitatively different if machines interact with human participants.

@article{ego,
    title = {{Integrating machine behavior into human subject experiments: a user-friendly toolkit and an application to framed prisoner's dilemmas}},
    author = {Engel, Christoph and Grossmann, Max~R.~P. and Ockenfels, Axel},
    journal = {Experimental Economics},
    year = {2025},
    volume = {28},
    number = {5},
    pages = {1085--1100},
    month = sep,
    publisher = {Cambridge University Press},
    doi = {10.1017/eec.2025.10038},
    keywords = {mrpg},
}

Management Science (2024), 70(3):1343-1356 · Journal version · Citation

@article{fivsar2024reproducibility,
    title = {{Reproducibility in {\it Management Science}}},
    author = {Fi{\v{s}}ar, Milo{\v{s}} and Greiner, Ben and Huber, Christoph and Katok, Elena and Ozkes, Ali I. and {Management Science Reproducibility Collaboration}},
    journal = {Management Science},
    year = {2024},
    volume = {70},
    number = {3},
    pages = {1343--1356},
    publisher = {Informs},
    doi = {10.1287/mnsc.2023.03556},
    keywords = {mrpg},
}

Journal of Behavioral and Experimental Finance (2020) · Journal version · Abstract · Citation

We present z-Tree unleashed, a novel approach and set of scripts to aid the implementation of computerized behavioral experiments outside the laboratory. z-Tree unleashed enables subjects to join the experiment using a web portal that requires no software apart from a web browser. Experimenters are likewise enabled to administer their experiments from anywhere in the world. Except for z-Tree itself, z-Tree unleashed is entirely based on free and open-source software. In this paper we give a high-level overview of z-Tree unleashed’s features and benefits and its design. We also show how to set up the server and demonstrate the steps required for conducting an entire experiment. We subsequently explain how to leverage the security and routing features of a virtual private network with z-Tree unleashed, enabling servers to securely run behind routers.

@article{zTu,
    title = {{{\it z-Tree unleashed}: A novel client-integrating architecture for conducting z-Tree experiments over the Internet}},
    author = {Duch, Matthias L. and Grossmann, Max~R.~P. and Lauer, Thomas},
    journal = {Journal of Behavioral and Experimental Finance},
    year = {2020},
    volume = {28},
    pages = {100400},
    publisher = {Elsevier},
    doi = {10.1016/j.jbef.2020.100400},
    url = {https://www.sciencedirect.com/science/article/pii/S2214635020303270},
    issn = {2214-6350},
    keywords = {mrpg},
}

Website · Demo · Abstract · Citation

Existing popular software frameworks for conducting behavioral experiments—both online and in the lab—suffer from limitations including architectural inflexibility and limited feature sets that restrict their utility. They are closed source or do not encourage outside contributions. To overcome these restrictions, we introduce “uproot”: a scalable, genuinely open-source framework for developing and conducting behavioral experiments. uproot revolutionizes data storage with an append-only log, ensuring data persistence and allowing the use of arbitrary data types. uproot provides many additional important features for modern experiments. For example, Likert scales are provided out of the box, file uploads are possible, and internal pages can be customized easily. With capabilities such as page repetition, random page orderings, indefinitely repeated sets of pages, management of individual subjects, dynamically sized sessions, and convenient async-first APIs, uproot overcomes many of the limitations of existing frameworks. Our framework is suited for both small-scale and large-scale studies, including surveys and experiments in which participants interact with each other. We encourage community-driven development.

@unpublished{uproot,
    title = {{uproot: A Software Framework for Behavioral Experiments}},
    author = {Grossmann, Max~R.~P. and Gerhardt, Holger},
    year = {2026},
    url = {https://uproot.science},
    note = {Unpublished manuscript},
    keywords = {mrpg},
}

Revision requested · Working paper · Replication package · Abstract · Citation

Mandatory waiting periods have been instituted for medical procedures, gun purchases, and other high-stakes decisions. Are these softly paternalistic policies substitutes for harder restrictions, and are delayed decisions more respected? In a general population survey experiment, Choice Architects make rules for decision-makers facing a high-stakes Bomb Risk Elicitation Task. Treatments vary when the decision is made: on the spot or after one day, and whether the initial decision can be revised. Choice Architects set a cap on the decision-maker's risk taking; in one treatment, they can additionally implement a mandatory waiting period. Exogenous deliberation has no effect on the cap; equivalence testing (TOST) and Bayesian analysis (BF₀₁ ≈ 12) provide strong positive evidence for the absence of an effect. Endogenously prescribed waiting periods are add-on restrictions that do not substitute for the cap. Choice Architects believe that, with time, the average decision-maker will take less risk and—because of the distribution of Choice Architects' bliss points—come closer to Choice Architects' subjective ideal choice; the resulting reduction in forecasted errors is small. Soft and hard paternalistic instruments are not substitutes: waiting periods are deployed as add-on restrictions.

@misc{undo,
    title = {{Paternalism and Deliberation: An Experiment on Making Formal Rules}},
    author = {Grossmann, Max~R.~P.},
    year = {2026},
    eprint = {2501.00863v2},
    archivePrefix = {arXiv},
    primaryClass = {econ.GN},
    url = {https://arxiv.org/abs/2501.00863v2},
    keywords = {mrpg},
}

Under review · Working paper · Replication package · Abstract · Citation

When environmental regulations face resistance, policymakers often assume information deficits drive opposition. We test this idea in the context of a major climate policy: Germany's Heating Law of 2023, which mandates the phase-out of fossil fuel heating. Through a high-powered survey experiment with property owners, we examine whether providing comprehensive information about the regulation's costs, requirements, and timeline affects adoption decisions and policy support. Although information provision significantly increases factual knowledge, it does not significantly affect intended technology adoption, policy support, or incentivized measures of climate preferences. For comprehensive information, the standardized effect on policy support is −0.02 (90% CI: [−0.11, 0.06]). Using treatment-induced variation in knowledge, the estimated effect of one additional correct answer is −0.05 points on the five-point support scale (95% CI: [−0.20, 0.10]). Pre-existing environmental preferences and demographic characteristics better predict responses to the regulation. Cost considerations and perceived functionality of existing systems drive non-adoption among fossil fuel users, while independence from fossil fuels and collective benefits motivate adoption among switchers. Our findings suggest that policy opposition may stem more from preference heterogeneity than information gaps, with implications for the design of behavioral interventions in environmental policy.

@misc{heizg,
    title = {{Public Support for Environmental Regulation: When Ideology Trumps Knowledge}},
    author = {Dertwinkel-Kalt, Markus and Grossmann, Max~R.~P.},
    year = {2025},
    month = sep,
    url = {https://q.mg.sb/heizg},
    note = {Working paper},
    keywords = {mrpg},
}

Working paper · Replication package · Abstract · Citation

When is autonomy granted to a decision-maker based on their knowledge, and if no autonomy is granted, what form will the intervention take? A parsimonious theoretical framework shows how policymakers can exploit decision-maker mistakes and use them as a justification for intervention. In two experiments, policymakers ("Choice Architects") can intervene in a choice faced by a decision-maker. We vary the amount of knowledge decision-makers possess about the choice. Full decision-maker knowledge causes more than a 60% reduction in intervention rates. Beliefs have a small, robust correlation with interventions on the intensive margin. Choice Architects disproportionately prefer to have decision-makers make informed decisions. Interveners are less likely to provide information. As theory predicts, the same applies to Choice Architects who believe that decision-maker mistakes align with their own preference. When Choice Architects are informed about the decision-maker's preference, this information is used to determine the imposed option. However, Choice Architects employ their own preference to a similar extent. A riskless option is causally more likely to be imposed, being correlated with but conceptually distinct from Choice Architects' own preference. This is a qualification to what has been termed "projective paternalism."

@misc{knf0,
    title = {{Knowledge and Freedom: Evidence on the Relationship Between Information and Paternalism}},
    author = {Grossmann, Max~R.~P.},
    year = {2024},
    eprint = {2410.20970v2},
    archivePrefix = {arXiv},
    primaryClass = {econ.GN},
    url = {https://arxiv.org/abs/2410.20970v2},
    keywords = {mrpg},
}

ORDO (2026), 75(1):279-282 · Open-access article · Abstract · Citation

Lachmann (1963) entwickelt eine Typologie wirtschaftlicher Institutionen: Äußere Institutionen (Eigentumsrecht, Vertragsrecht) bilden das erzwingbare Rahmenwerk der Marktwirtschaft. Innere Institutionen (Börsen, Versicherungen) entstehen aus Marktprozessen heraus und passen sich kontinuierlich an. Neutrale Institutionen (Tarifvertragswesen, Arbeitsnachweise) werden staatlich bereitgestellt; ihre Nutzung ist formal freiwillig. Am Beispiel der kollektiven Lohnfestsetzung zeigt Lachmann das Kernproblem: Das „Axiom“ nie fallender Löhne führt zu permanenter Inflation und untergräbt die Geldordnung. Während innere Institutionen durch Marktmechanismen zur Kohärenz tendieren, fehlt äußeren und neutralen Institutionen diese integrierende Kraft.

@article{lachmann-kommentar,
    title = {{Lachmann, L.\ M.\ (1963): Wirtschaftsordnung und wirtschaftliche Institutionen -- Kommentar}},
    author = {Grossmann, Max~R.~P.},
    journal = {ORDO},
    year = {2026},
    volume = {75},
    number = {1},
    pages = {279--282},
    month = jul,
    doi = {10.1515/ordo-2026-2021},
    url = {https://doi.org/10.1515/ordo-2026-2021},
    issn = {0048-2129},
    langid = {german},
    keywords = {mrpg},
}

I4R Discussion Paper Series, No. 295 (2026) · Published version · Citation

@techreport{gambler-replication,
    title = {{Replication Report: On the Robustness and Provenance of the {Gambler's Fallacy} by Xiang, Dorst, and Gershman (2025)}},
    author = {{van den Berg}, Anthony and Doroc, Karlo and Fu, Changfa and Grossmann, Max~R.~P. and Miller, Joshua B. and Pavlovic, Lana},
    year = {2026},
    type = {I4R Discussion Paper Series},
    number = {295},
    institution = {Institute for Replication. Prepared during the 2025 Melbourne Replication Games at the University of Melbourne},
    url = {https://hdl.handle.net/10419/341114},
    keywords = {mrpg},
}

Kölner Impulse zur Wirtschaftspolitik (2025), 2025(3):3-14 · Journal version · Official English translation · Abstract · Citation

In diesem Impuls analysiert Max R. P. Grossmann paternalistische Tendenzen in der deutschen Wirtschaftspolitik. Er beleuchtet zunächst theoretische Grundlagen von Freiheitseinschränkungen durch paternalistische Eingriffe und illustriert diese anhand konkreter gesetzlicher Regelungen – vom Arbeitszeitgesetz bis zur Glücksspielregulierung. Aufbauend auf empirischer Forschung und experimentellen Studien zeigt er, wie und warum Menschen Entscheidungen für andere treffen. Abschließend plädiert er für eine smarte, differenzierte Regulierung, die individuelle Autonomie respektiert und paternalistische Eingriffe auf das notwendige Maß begrenzt.

@article{impuls,
    title = {{Schutz vor sich selbst? Paternalistische Versuchungen deutscher Wirtschaftspolitik}},
    author = {Grossmann, Max~R.~P.},
    journal = {K{\"o}lner Impulse zur Wirtschaftspolitik},
    year = {2025},
    number = {3},
    pages = {3--14},
    publisher = {Institut f{\"u}r Wirtschaftspolitik an der Universit{\"a}t zu K{\"o}ln},
    langid = {german},
    keywords = {mrpg},
}

Wirtschaftsdienst (2025), 105(7):495-498 · Journal version · Coverage in Altpapier (2025) · Abstract · Citation

In der politischen Debatte über Klimapolitik ist ein Argument allgegenwärtig: Wenn Bürger:innen nur besser informiert wären, dann würden sie auch zustimmen. Widerstände gegen Gesetzesvorhaben wie das deutsche Gebäudeenergiegesetz (GEG) gelten häufig als Folge mangelnder Kommunikation – nicht etwa als Ausdruck grundsätzlicher Ablehnung. Doch trifft diese Annahme tatsächlich zu? Eine neue Studie mit 2.668 Eigentümer:innen von Wohnimmobilien in Deutschland geht dieser Frage im Rahmen eines Umfrageexperiments nach. Erhöhen sachlich korrekte und umfassende Informationen über das GEG die Zustimmung zur Maßnahme und beeinflussen sie das Verhalten? Das zentrale Ergebnis überrascht: Information allein reicht nicht aus – die Akzeptanz hängt vielmehr maßgeblich von den ideologischen Grundüberzeugungen der Befragten ab. Diese Erkenntnis ist insbesondere für wirtschaftspolitische Entscheidungsträger relevant, die vor der Herausforderung stehen, transformative Klimapolitik zu gestalten und durchzusetzen.

@article{heizg-wd,
    title = {{Ideologie schl{\"a}gt Information: {\"U}ber die Grenzen von Kommunikation in der Klimapolitik}},
    author = {Dertwinkel-Kalt, Markus and Grossmann, Max~R.~P.},
    journal = {Wirtschaftsdienst},
    year = {2025},
    volume = {105},
    number = {7},
    pages = {495--498},
    month = jul,
    doi = {10.2478/wd-2025-0129},
    url = {https://www.wirtschaftsdienst.eu/index.php/inhalt/jahr/2025/heft/7/beitrag/ideologie-schlaegt-information-ueber-die-grenzen-von-kommunikation-in-der-klimapolitik.html},
    issn = {0043-6275},
    langid = {german},
    keywords = {mrpg},
}

Computation (world record, 2017). Download (sig) · Coverage in Spektrum (2025) · Abstract

See here for further information. The previous world record computation (from 2013, also by me) can be downloaded here.