Research Group Helmut Küchenhoff

Understanding how assignments of instances to clusters can be attributed to the features can be vital in many applications. However, research to provide such feature attributions has been limited. Clustering algorithms with built-in explanations are scarce. Common algorithm-agnostic approaches involve dimension reduction and subsequent visualization, which transforms the original features used to cluster the data; or training a supervised learning classifier on the found cluster labels, which adds additional and intractable complexity. We present FACT (feature attributions for clustering), an algorithm-agnostic framework that preserves the integrity of the data and does not introduce additional models. As the defining characteristic of FACT, we introduce a set of work stages: sampling, intervention, reassignment, and aggregation. Furthermore, we propose two novel FACT methods: SMART (scoring metric after permutation) measures changes in cluster assignments by custom scoring functions after permuting selected features; IDEA (isolated effect on assignment) indicates local and global changes in cluster assignments after making uniform changes to selected features.

The association between protein intake and the need for mechanical ventilation (MV) is controversial. We aimed to investigate the associations between protein intake and outcomes in ventilated critically ill patients.

Age-Period-Cohort (APC) analysis aims to determine relevant drivers for long-term develop- ments and is used in many fields of science (Yang & Land, 2013). The R package APCtools offers modern visualization techniques and general routines to facilitate the interpretability of the interdependent temporal structures and to simplify the workflow of an APC analysis. Separation of the temporal effects is performed utilizing a semiparametric regression approach. We shortly discuss the challenges of APC analysis, give an overview of existing statistical software packages and outline the main functionalities of the package.

This dissertation develops new approaches for robustly estimating functional data structures and analyzing age-period-cohort (APC) effects, with applications in seismology and tourism science. The first part introduces a method that separates amplitude and phase variation in functional data, adapting a likelihood-based registration approach for generalized and incomplete data, demonstrated on seismic data. The second part presents generalized functional additive models (GFAMs) for analyzing associations between functional data and scalar covariates, along with practical guidelines and an R package. The final part addresses APC analysis, proposing new visualization techniques and a semiparametric estimation approach to disentangle temporal dimensions, with applications to tourism data, and is supported by the APCtools R package. (Shortened.)

This study investigates how age, period, and birth cohorts are related to altering travel distances. We analyze a repeated cross-sectional survey of German pleasure travels for the period 1971–2018 using a holistic age–period–cohort (APC) analysis framework. Changes in travel distances are attributed to the life cycle (age effect), macro-level developments (period effect), and generational membership (cohort effect). We introduce ridgeline matrices and partial APC plots as innovative visualization techniques facilitating the intuitive interpretation of complex temporal structures. Generalized additive models are used to circumvent the identification problem by fitting a bivariate tensor product spline between age and period. The results indicate that participation in short-haul trips is mainly associated with age, while participation in long-distance travel predominantly changed over the period. Generational membership shows less association with destination choice concerning travel distance. The presented APC approach is promising to address further questions of interest in tourism research.