NLP research frequently grapples with multiple sources of variability—spanning runs, datasets, annotators, and more—yet conventional analysis methods often neglect these hierarchical structures, threatening the reproducibility of findings. To address this gap, we contribute a case study illustrating how linear mixed-effects models (LMMs) can rigorously capture systematic language-dependent differences (i.e., population-level effects) in a population of monolingual and multilingual language models. In the context of a bilingual hate speech detection task, we demonstrate that LMMs can uncover significant population-level effects—even under low-resource (small-N) experimental designs—while mitigating confounds and random noise. By setting out a transparent blueprint for repeated-measures experimentation, we encourage the NLP community to embrace variability as a feature, rather than a nuisance, in order to advance more robust, reproducible, and ultimately trustworthy results.

This work investigates capturing and modeling disagreement in Semantic Textual Similarity (STS), where sentence pairs are assigned ordinal similarity labels (0–5). Conventional STS systems average multiple annotator scores and focus on a single numeric estimate, overlooking label dispersion. By leveraging the disaggregated SemEval-2015 dataset (Soft-STS-15), this paper proposes and compares two disagreement-aware strategies that treat STS as an ordinal distribution prediction problem: a lightweight truncated Gaussian head for standard regression models, and a cross-encoder trained with a distance-aware objective, refined with temperature scaling. Results show improved performance in distance-based metrics, with the calibrated soft-label model proving best overall and notably more accurate on the most ambiguous pairs. This demonstrates that modeling disagreement benefits both calibration and ranking accuracy, highlighting the value of retaining and modeling full annotation distributions rather than collapsing them to a single mean label.