Yannis Bähni | Searcharxiv

arXiv2026

A Bayesian Approach to Estimating Effect Sizes in Educational Research

In this paper, we demonstrate a purely Bayesian approach for estimating within-group and between-group effect sizes for learning outcomes encountered in educational research, taking naturally into account the multilevel structure of the data, as well as heterogeneous residual variances among time points and conditions. We provide a detailed implementation using the brms package in R serving as a wrapper for the probabilistic programming language Stan. We recommend that for a pooled design, one computes an effect size $d_s$ similar to a Cohen's $d$, and for a paired design, one should compute two possibly different quantities $d_s$ and $d_z$ to correct for correlations in within-group designs and allow for comparability across different studies. All these effect sizes are based on ideas coming from Hedge's total effect size $δ_t$ introduced in 2007. Ultimately, these estimates allow us to study the differential effectiveness of educational interventions with respect to classes.

stat.AP↗

arXiv2024

On a Theorem by Schlenk

In this paper we prove a generalisation of Schlenk's theorem about the existence of contractible periodic Reeb orbits on stable, displaceable hypersurfaces in symplectically aspherical, geometrically bounded, symplectic manifolds, to a forcing result for contractible twisted periodic Reeb orbits. We make use of holomorphic curve techniques for a suitable generalisation of the Rabinowitz action functional in the stable case in order to prove the forcing result. As in Schlenk's theorem, we derive a lower bound for the displacement energy of the displaceable hypersurface in terms of the action value of such periodic orbits. The main application is a forcing result for noncontractible periodic Reeb orbits on quotients of certain symmetric star-shaped hypersurfaces. Either there exist two geometrically distinct noncontractible periodic Reeb orbits or the period of the noncontractible periodic Reeb orbit is small. This theorem can be applied to many physical systems including the Hénon-Heiles Hamiltonian and Stark-Zeeman systems. Further applications include a new proof of the well-known fact that the displacement energy is a relative symplectic capacity on $\mathbb{R}^{2n}$ and that the Hofer metric is indeed a metric.

math.SG↗

arXiv2022

Lectures on Twisted Rabinowitz-Floer Homology

Rabinowitz-Floer homology is the Morse-Bott homology in the sense of Floer associated with the Rabinowitz action functional introduced by Kai Cieliebak and Urs Frauenfelder in 2009. In this manuscript, we consider a generalisation of this theory to a Rabinowitz-Floer homology of a Liouville automorphism. As an application, we show the existence of noncontractible periodic Reeb orbits on quotients of symmetric star-shaped hypersurfaces. In particular, this theory applies to lens spaces. Moreover, we prove a forcing theorem, which guarantees the existence of a contractible twisted closed characteristic on a displaceable twisted stable hypersurface in a symplectically aspherical geometrically bounded symplectic manifold if there exists a contractible twisted closed characteristic belonging to a Morse-Bott component, with energy difference smaller or equal to the displacement energy of the displaceable hypersurface.

math.SG↗

arXiv2021

First Steps in Twisted Rabinowitz-Floer Homology

Rabinowitz-Floer homology is the Morse-Bott homology in the sense of Floer associated with the Rabinowitz action functional introduced by Kai Cieliebak and Urs Frauenfelder in 2009. In our work, we consider a generalisation of this theory to a Rabinowitz-Floer homology of a Liouville automorphism. As an application, we show the existence of noncontractible periodic Reeb orbits on quotients of symmetric star-shaped hypersurfaces. In particular, our theory applies to lens spaces.

math.SG↗