Abstract

When poor reproducibility in preclinical animal research is discussed, the usual suspects appear quickly: weak design, small sample sizes, publication bias. These matter. But another driver may be equally important: biological variation. This is not random noise. It reflects genetic background, environmental influences, and their interaction. Each animal enters an experiment with a distinct genetic and environmental profile that modulates its physiological response to an intervention. When experiments are designed around extreme standardization and aim to eliminate this variation, findings may become valid only under very narrow lab conditions. By contrast, study designs that deliberately incorporate controlled heterogeneity can improve external validity, strengthen reproducibility, and reduce the need for endless follow-up studies that never quite confirm the original result. Robust science does not remove variation. It understands it, and designs with it in mind. 

Reference list: 

1. Voelkl, Bernhard; Lucile Vogt; Emily S. Sena; Hanno Würbel. Reproducibility of preclinical animal research improves with heterogeneity of study samples. PLOS Biology. 2018;16(2):e2003693. doi:10.1371/journal.pbio.2003693

2. Voelkl, Bernhard; Naomi S. Altman; Anders Forsman; Wolfgang Forstmeier; Jessica Gurevitch; Ivana Jaric; Natasha A. Karp; Martien J. Kas; Holger Schielzeth; Tom Van de Casteele; Hanno Würbel. Reproducibility of animal research in light of biological variation. Nature Reviews Neuroscience. 2020;21(7):384–393. doi:10.1038/s41583-020-0313-3

Learning outcomes

• Distinguish biological variation from random noise

• Explain how standardization can limit external validity

• Identify sources of heterogeneity in animal studies

• Apply design strategies that incorporate controlled variation

• Strengthen robustness and translatability in study planning