Philipp Külpmann

Assistant Professor, Institute of Economics, Corvinus University of Budapest and
Affiliated Member, Vienna Center for Experimental Economics, University of Vienna

philipp.kulpmann@uni-corvinus.hu

CV

My research interest lies primarily in Experimental Economics and Game Theory.
Currently, I am organizing the Budapest Experimental and Behavioral Economics (BEBE) Seminar.

Publications

Working papers

  • Aggregate Nash Attainability and Boundary Equilibria under Behavioral Heterogeneity, with Wieland Müller and Alexander K. Wagner.
    We study which Nash equilibria of a finite normal-form game can still arise as aggregate play when each player role is represented by a population containing both behavioral and optimizing agents. In each role, a fixed fraction of agents follows an exogenous action distribution, while the remaining agents best respond to aggregate play. A Nash equilibrium survives if and only if, for every role and every action, the behavioral mass assigned to that action does not exceed its Nash equilibrium probability. When this condition holds, optimizing agents choose the residual distribution and aggregate play reproduces the original Nash equilibrium. When it fails, behavioral types assign too much probability mass to some action, and exact aggregate recovery is impossible. We further show that any additional aggregate equilibria generated by behavioral heterogeneity must lie on the boundary of the aggregate-feasible set and are sustained by behavioral types playing non-optimal actions. Behavioral heterogeneity may thus prune some Nash equilibria and create genuinely new ones, and we characterize both.
  • When Decoys Fail: Evidence from Video Game Edition Choice, with Fábián Garas and Botond Ujvári and Andreas Orland.
    We study whether classic decoy effects generalize to a consequential digital marketplace setting. In a preregistered, incentivized online field experiment designed to resemble the Steam storefront, 435 participants repeatedly chose between a cheaper base video game edition and a more expensive target edition, with or without a third option constructed as an attraction or compromise decoy. Contrary to standard decoy predictions, neither decoy increased target choice in the full sample. Decoys were themselves chosen at nontrivial rates, and descriptive, non-inferiority, and regression analyses indicate small, null, or opposite-direction effects when decoy choosers are excluded. The results suggest that familiar, information-rich, and consequential platform settings can substantially weaken classical decoy effects. More broadly, the paper shows that choice architecture in digital markets should be tested in the environments in which it is intended to operate.
  • Playing Prisoner's Dilemma Games with a Large Language Model, with Andreas Orland and Kazuhiro Takemoto.
    We report results from a large-scale, laboratory-style experiment in which a Large Language Model (LLM)-represented by three versions of ChatGPT-3.5-turbo—makes decisions and forms beliefs about the behavior of other players in a one-shot Prisoner’s Dilemma (PD). We independently manipulate four dimensions of the game in a full factorial design: (i) all four payoff parameters, (ii) the number of simultaneous interaction partners, (iii) the available strategy space, and (iv) the order of eliciting decisions and beliefs. On average, the LLM is highly cooperative (≈79%), whereas its stated beliefs about others’ cooperation are much lower (≈48%). Variations in payoffs have negligible effects on model behavior, whereas the other dimensions shift cooperation rates and beliefs in directions consistent with classic findings from experiments with human subjects. We further find that decisions and beliefs are highly correlated. Regressions show that the LLM’s responses are highly predictable.
  • Coordination without Common Knowledge: Separating First- and Higher-Order Belief Failures, with Davit Khantadze.
    We investigate the effect of absence of common knowledge on the outcomes of coordination games in a laboratory experiment. Using cognitive types, we can explain coordination failure in pure coordination games while differentiating between coordination failure due to first- and higher-order beliefs. In our experiment, around 76% of the subjects have chosen the payoff-dominant equilibrium strategy despite the absence of common knowledge. However, 9% of the players had first-order beliefs that lead to coordination failure and another 9% exhibited coordination failure due to higher-order beliefs. Furthermore, we compare our results with predictions of commonly used models of higher-order beliefs.

In progress

Contact

Office

Building E, room 239 (2nd floor)

Postal Address

Philipp Külpmann
Institute of Economics
Fővám tér 8
1093 Budapest, Hungary