# Born to Win? The Hidden Bias of Birthdates in Spanish Orienteering Talent Selection
## 2 Materials and Methods
### Participants  
The sample comprised all Spanish orienteering athletes holding a national licence who were selected to represent Spain in international competitions organised by the International Orienteering Federation (IOF) between 1987 and 2023 (\(n=252\); 103 women and 149 men). Records lacking birthdate information (11 women and 19 men) were excluded. The events considered were the European Youth Orienteering Championships (EYOC), the Junior World Orienteering Championships (JWOC), the European Orienteering Championships (EOC), and the World Orienteering Championships (WOC). To avoid overrepresentation of individual athletes due to repeated selections, only one participation per athlete per event type was considered. This yielded a total of 384 participation records (159 for the female group and 225 for the male group). This approach ensured the independence of observations. It also prevented repeated performances from disproportionately influencing the birthdate distribution, thereby enhancing the robustness of the statistical analysis. It is important to note that this approach focused on identifying the RAE's influence on selection into different international competition tiers (EYOC, JWOC, EOC + WOC) by considering one selection per athlete per event type. While this ensured the independence of observations and robustness of the statistical analysis regarding birthdate distribution within each competition type, it did not account for the frequency of selection across multiple competition types or across different years for the same event. Therefore, it does not distinguish between athletes experiencing 'continuous selection' versus 'one-time selection', which could offer additional insights into long-term athlete development. Future research could explore these aspects to provide a more comprehensive understanding of selection patterns. The data were further segmented by type of event and competitive group (female or male), as shown in Table 1. As can be observed, WOC and EOC participations are presented jointly since they alternate biennially and never occur in the same year. Grouping them increased the sample size and improved statistical power. Data were obtained from the Lithuanian database portal DB Sportas (n.d. Lithuanian Orienteering Federation, Vilnius, Lithuania), which provides historical records of participation in IOP events from their inaugural editions: WOC since 1966; JWOC since 1990; EYOC since 1999; and EOC since 2000. In the case of Spain, participation records are available for WOC from 1987 onwards, while EYOC, JWOC, and EOC data are available from their respective first editions. To ensure data accuracy, records were cross-checked with those published by the Spanish Orienteering Federation (FEDO) and the IOF. In the EYOC, the IOF defines two biennial age-group categories for athletes aged 16 to 18: W/M-16 and W/M-18 (W = Women; M = Men). In the JWOC, athletes aged 19-20 compete in a single W/M-20 category. At the senior level (EOC and WOC), there are only two absolute categories: one for women and one for men. To compare the selected athletes with the total population of licensed orienteers in Spain, data from previous research [1] were used (Table 2). Specifically, athletes selected for EYOC were compared to the F/M-16 and F/M-18 groups; those selected for JWOC were compared to F/M-20; and those selected for WOC and EOC were compared to the elite category (F/M-E). Furthermore, for the EYOC event, it is important to acknowledge that the data combine W/M-16 and W/M-18 age groups as defined by the IOF's biennial categorization system. While this grouping was necessary to achieve a sufficient sample size for analysis given the historical data, it introduces a broader chronological age range within the youth sample. The combination of these age groups might potentially influence the manifestation of age-related differences in selection, a factor that should be considered when interpreting the EYOC results.