Forever young: Relative age effects in Belgian political selection

Political selection is crucial for the functioning of democracy. However, the practice—in education and sports contexts—of artificially dividing school-age children into different age groups leads to a considerable bias in this selection. The probability of becoming a (successful) politician depends on individuals' relative age. Being born shortly after the cut-off date significantly increases the probability that an individual will be politically successful later in life. Using a regression discontinuity design, we find strong evidence of such relative age effect (RAE) among a large sample of Belgian federal parliamentarians over the period 1950–2019 (N = 4032), but not among municipal councillors (N = 7387), nor among municipal candidates (N = 36,740) in the 2018 election. The estimated overrepresentation of federal members of the parliament (MPs) born immediately after the cut-off date is up to 90% compared to politicians born just before the cut-off date. The overrepresentation is observed over the whole period and thus seems to be deeply rooted in the political system. We find the RAE to have a gendered dimension: The effect is driven by early-born male politicians' overrepresentation. No significant RAE was found among female politicians.