Resampling Methods for Class Imbalance in Clinical Prediction Models: A Systematic Review and Meta-Regression Protocol

IntroductionClass imbalance--situations where clinically important "positive" cases form <30 % of the dataset--systematically degrades the sensitivity and fairness of medical prediction models. Although data-level techniques such as random oversampling, random undersampling and SMOTE, and algorithm-level approaches like cost-sensitive learning, are widely used, the empirical evidence describing when these corrections improve model performance remains fragmented across diseases and modelling frameworks. This protocol outlines a scoping systematic review with meta-regression that will map and quantitatively summarise 15 years of research on resampling strategies in imbalanced clinical datasets, addressing a critical methodological gap in trustworthy medical AI. Methods and analysisWe will search MEDLINE, EMBASE, Scopus, Web of Science Core Collection and IEEE Xplore, plus grey-literature sources (medRxiv, arXiv, bioRxiv) for primary studies (2009 - 31 Dec 2024) that apply at least one resampling or cost-sensitive method to binary clinical prediction tasks with a minority-class prevalence <30 %. No language restrictions will be applied. Two reviewers will screen records, extract data with a piloted form and document the process in a PRISMA flow diagram. A descriptive synthesis will catalogue clinical domain, sample size, imbalance ratio, resampling technique, model type and performance metrics where[&ge;]10 studies report compatible AUCs, a random-effects mixed-effects meta-regression (logit-transformed AUC) will examine moderators including imbalance ratio, resampling class, model family and sample size. Small-study effects will be probed with funnel plots, Eggers test, trim-and-fill and weight-function models; influence diagnostics and leave-one-out analyses will assess robustness. Because this is a methodological review, formal clinical risk-of-bias tools are optional; instead, design-level screening, influence diagnostics and sensitivity analyses will ensure transparency. DiscussionBy combining a broad conceptual map with quantitative estimates, this review will establish when data-level versus algorithm-level balancing yields genuine improvements in discrimination, calibration and cost-sensitive metrics across diverse medical domains. The findings will guide researchers in choosing parsimonious, evidence-based imbalance corrections, inform journal and regulatory reporting standards, and highlight research gaps, such as the under-reporting of calibration and misclassification costs, that must be addressed before balanced models can be trusted in clinical practice. Systematic review registrationINPLASY202550026