Relative age effect in formal musical training

Access to musical training depends on various factors, such as socioeconomic status and musical background of families, and the child's interest in learning music (related to their openness to experience). In the present study, we show an additional source of selection bias that has gone unnoticed: the relative age of children within the same cohort. At early ages, children at different stages of cognitive and physical development are placed in the same group, in part because of the relative age difference (up to nearly 12 months). The consequences of this grouping are known as the relative age effect, ranging from academic outcomes, self-esteem, and selection of extracurricular activities. In youth sports, there has been observed an overrepresentation of athletes born in the first and second birth quarters compared to those born later. This study shows a similar unbalance across Spanish music conservatory courses in two samples: a Primary Sample of participants assessed by our research group (N = 322) and a Secondary Sample comprised by the complete census of six conservatories in Spain (N = 2182). In our sample, the relative age of the children and adolescents was an independent predictor of the other selection bias factors evaluated. Moreover, the relative age effect was stable across conservatory courses, pointing to an enrolment bias and the impact of a lack of adjustment in the conservatory entrance exam. Future research will shed light on the origins of the relative age effect in musical training, its extension, and how it can be mitigated.