Editorial: Reporting baseline variables - descriptive summaries rather than inferential comparisons: editorial series on improving reporting and methodological rigor in scientific articles

Baseline characteristics describe the preexposure or pre-intervention properties of a study sample and are intended to inform interpretation and the assessment of comparability, rather than to support inferential comparisons beyond what was observed. Baseline variables should be pre-specified and justified in the study protocol, guided by clinical relevance, established reporting standards and frameworks, and presented in a dedicated table following the study flow diagram. Continuous variables should be summarized as means with standard deviations or, when skewed, medians with interquartile ranges; categorical variables as counts with proportions, reported separately by comparison group with absolute numbers and indication of missingness. In randomized trials, significance testing of baseline differences is not recommended, as any observed differences arise by chance. In cohort studies, baseline comparisons should be interpreted descriptively as evaluations of group comparability and the potential for confounding; standardized differences are preferred for quantifying imbalance. By complementing existing reporting standards and addressing common deficiencies, this guidance supports consistent, reproducible reporting of baseline variables and clearer communication of study populations.