Relative age effects in Rugby union and Rugby league: a systematic review and meta-analysis

Introduction Relative Age Effects (RAEs) are prominent factors affecting youth sport participation and talent identification and selection processes. In rugby, RAEs appear to be prevalent in both Rugby League (RL) and Rugby Union (RU), yet no study has quantitatively synthesised the available evidence across codes. This systematic review and meta-analysis aimed to identify RAE prevalence, magnitude, and moderating factors (i.e., sex, age, and competition level) across rugby codes, using the extreme-quartile contrast between Q1 and Q4. Methods A systematic search in CINAHL, Ovid, PsycINFO, PubMed, Scopus, and Web of Science identified 26 eligible studies. Distribution data were synthesised using odds ratio meta-analyses with an inverse-variance random-effects model and separate analyses by sex, age, and competition level. Results Male players showed a significant overrepresentation in Q1 vs. Q4 (34.8% vs. 16.9%; OR = 1.99), with smaller but similar effects in female players (27.5% vs. 23.6%; OR = 1.15). In males, RAEs were stronger in youth than senior categories (OR = 2.42 vs. 1.41), and in younger (U7–U14; U15–U17) vs. older age groups (U18-U20). Discussion Descriptively, RAEs appeared larger at higher competition levels, particularly in youth males (regional/Local: OR = 2.14; national: OR = 2.76). Overall, findings demonstrate that RAEs are pervasive in rugby and persist across sex, age, and competition level. However, the magnitude of the pooled estimates should be interpreted cautiously in light of the substantial between-study heterogeneity and the attenuation of the male effect following adjustment.