The relative age effect in soccer: a case study of the São Paulo Football Club

The aim of this study was to compare the birth-date distribution of youth athletes of a high-level Brazilian soccer club with the general population of the same age group. In a cross-sectional study, the birth date of 341 youth athletes (under 10-20) was compared with a reference population (live births that occurred in São Paulo state in the same age group; n = 5,480,868). The subjects were divided into quarters of birth: 1st = January-March; 2nd = April-June; 3rd = July-September; 4th = October-December. The chi-square test (χ2) was used to compare the expected (reference population) and observed (athletes) distributions. It was detected a significant difference between the expected distribution and observed distribution (χ2= 29.53; p