## 3 Results
Figure 1: Bar chart representing the birth date distribution (%) by semester (S1 and S2) of the total population of Total Federated athletes and the subgroups of young and elite athletes. Note: (F + M) = Total sample, female and male; (F) = female sample; (M) = male sample. * means \(p<0.05\). Table 6 presents the results of the odds ratio (OR) analysis and their corresponding 95% confidence intervals (CI 95%) for the comparisons between all birth quartiles in the different population groups studied. Pairwise quartile comparisons were performed using the \(Z\)-test, and the results align with the interpretations of the 95% confidence intervals calculated for the ORs. Therefore, in Table 6, the ORs whose 95% confidence intervals do not include the value 1 are marked with an asterisk (*), indicating significant differences between the compared quartile pairs, while the OR value indicates the effect magnitude. For instance, \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Age Groups** & **Q1 (\%)** & **Q2 (\%)** & **Q3 (\%)** & **Q4 (\%)** & **\(\chi\)2** & **\(p\)** & **V** \\ \hline U-10 & 31.84 & 22.63 & 25.42 & 20.11 & 12.601 & 0.006 & 0.19 \\ F-12 & 27.39 & 28.26 & 22.17 & 22.17 & 13.463 & 0.004 & 0.14 \\ F-14 & 25.74 & 28.32 & 20.30 & 25.64 & 19.885 & \textless{}0.001 & 0.14 \\ F-16 & 25.14 & 28.44 & 21.27 & 25.14 & 13.722 & 0.003 & 0.12 \\ F-18 & 30.93 & 24.08 & 21.79 & 23.20 & 15.032 & 0.002 & 0.16 \\ F-20 & 29.72 & 26.10 & 22.74 & 21.45 & 8.923 & 0.030 & 0.15 \\ F-Elite & 22.69 & 28.65 & 23.65 & 25.00 & 5.599 & 0.133 & 0.10 \\ M-12 & 26.08 & 29.67 & 24.13 & 20.12 & 24.088 & \textless{}0.001 & 0.16 \\ M-14 & 26.66 & 28.15 & 23.23 & 21.97 & 20.671 & \textless{}0.001 & 0.12 \\ M-16 & 26.01 & 26.17 & 24.23 & 23.59 & 5.983 & 0.112 & 0.07 \\ M-18 & 27.14 & 28.45 & 22.74 & 21.67 & 16.269 & 0.001 & 0.14 \\ M-20 & 26.56 & 28.04 & 24.04 & 21.36 & 10.221 & 0.017 & 0.12 \\ M-Elite & 30.92 & 25.59 & 17.89 & 25.59 & 38.516 & \textless{}0.001 & 0.21 \\ \hline \hline \end{tabular} Note. U-10 (<10 years); M/F-12 (11–12 years); M/F-14 (13–14 years); M/F-16 (15–16 years); M/F-18 (17–18 years); and M/F-20 (19–20 years), where M means “male” and F means “female”. Q1 = born in the first quarter of the year (January–March); Q2 = born in the second quarter of the year (April–June); Q3 = born in the third quarter of the year (July–September); Q4 = born in the fourth quarter of the year (October–December).  
\end{table} 
Table 5: Results of the Chi-square test (\(\chi\)2), significance values (\(p\)), and effect size (Cramer’s V) for the different age groups analyzed in relation to the quarterly distribution of births (Q): \(\chi\)2 (critical) = 7.8147 (\(p\) = 0.05). Figure 2: Bar chart representing the birth date distribution by semester (S1 and S2) for female athletes according to their age group and for athletes in the mixed U-10 group. (*) Statistically significant differences compared to athletes born in S1 (January–June), \(p\) < 0.05. In green, above each blue column (S1), the Cramer’s V value, indicative of the effect size, is shown for the S1/S2 relationship. in the male elite population group, Q1 shows a particularly strong overrepresentation compared to Q3 (OR = 2.054; CI = 1.65-2.56; Z = 6.371; \(p\) < 0.001).