{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T04:23:47Z","timestamp":1787027027942,"version":"build-2736575974"},"reference-count":39,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,5,28]],"date-time":"2026-05-28T00:00:00Z","timestamp":1779926400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Pharmacol."],"abstract":"<jats:p>\n                    The ethical imperative to reduce the use of animals in scientific experimentation has become increasingly prominent, driven by societal expectations, regulatory frameworks, and concerns regarding the reproducibility of preclinical research. While the principle of Reduction, one of the 3Rs originally defined by Russell and Burch, is widely endorsed, its practical implementation remains challenging. In particular, inappropriate experimental designs, inadequate statistical planning, and insufficient reporting standards continue to undermine both scientific validity and ethical justification, often leading either to the unnecessary use of animals or to underpowered studies whose results lack reliability. This review provides an updated and practical framework for determining the appropriate number of animals required in experimental biology and pharmacology. Building on earlier methodological recommendations, it emphasizes the central role of rigorous study planning, including the clear definition of objectives and primary endpoints, appropriate experimental design, randomization, blinding, and the judicious use of control groups. Special attention is given to factorial designs and the inclusion of interactions, which often allow substantial reductions in animal numbers without compromising statistical power. The review also discusses conditional procedures, pilot studies, interim analyses, and the frequent confusion between biological replicates, technical replicates, and true experimental replication. The statistical foundations of\n                    <jats:italic>a priori<\/jats:italic>\n                    sample size calculation are revisited, including the concepts of Type I and Type II errors, effect size, variability, and corrections for multiple comparisons. Practical guidance is provided for common experimental contexts, including comparisons of continuous and categorical outcomes, analysis of variance, survival analysis, pharmacokinetic and pharmacodynamic studies, and dose\u2013response experiments. Emerging approaches, such as sequential and Bayesian methods, are also discussed with respect to their potential for reduction and their limitations. Finally, this review highlights the ethical and scientific risks associated with excessive reduction leading to underpowered studies. It argues that optimal reduction does not mean using as few animals as possible, but rather using the right number, justified by sound experimental design and statistical reasoning. By promoting transparent planning and robust methodology, this work aims to support both ethical responsibility and scientific rigor in animal-based research.\n                  <\/jats:p>","DOI":"10.3389\/fphar.2026.1786234","type":"journal-article","created":{"date-parts":[[2026,5,28]],"date-time":"2026-05-28T10:06:26Z","timestamp":1779962786000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Reduce or not reduce: a practical guide to calculate sample size for various experimental design in studies involving animals"],"prefix":"10.3389","volume":"17","author":[{"given":"Jean Xavier","family":"Mazoit","sequence":"first","affiliation":[{"name":"Animal Ethics Committee CEEA26 (Comit\u00e9 d\u2019Ethique en Exp\u00e9rimentale Animale 26), Universit\u00e9 Paris-Saclay","place":["Villejuif, France"]},{"name":"Ex. Laboratoire d\u2019anesth\u00e9sie, Universit\u00e9 Paris-Saclay and INSERM U1195","place":["Villejuif, France"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Patrick","family":"Gonin","sequence":"additional","affiliation":[{"name":"Animal Ethics Committee CEEA26 (Comit\u00e9 d\u2019Ethique en Exp\u00e9rimentale Animale 26), Universit\u00e9 Paris-Saclay","place":["Villejuif, France"]},{"name":"Universit\u00e9 Paris-Saclay, Gustave Roussy, Inserm, Unit\u00e9 Analyse Mol\u00e9culaire et Imagerie de la Maladie Canc\u00e9reuse, Plateforme d\u2019Evaluation Pr\u00e9clinique, Comit\u00e9 d'Ethique n\u00b026","place":["Villejuif, France"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,5,28]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"2757","DOI":"10.3390\/ani12202757","article-title":"Identifying key factors for accelerating the transition to animal-testing-free medical science through co-creative, interdisciplinary learning between students and teachers","volume":"12","author":"Abarkan","year":"2022","journal-title":"Animals"},{"key":"B2","volume-title":"Your contribution to better science","year":"2025"},{"key":"B3","first-page":"pp175","volume-title":"Statistical methods in medical research","author":"Armitage","year":"1994"},{"key":"B4","volume-title":"Arrive Guidelines","year":"2025"},{"key":"B5","doi-asserted-by":"publisher","first-page":"289","DOI":"10.1111\/j.2517-6161.1995.tb02031.x","article-title":"Controlling the false discovery rate: a practical and powerful approach to multiple testing","volume":"57","author":"Benjamini","year":"1995","journal-title":"J. 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