47 Interim performance progression of talented swimmers 3 central limit theorem (Field, 1993). For n<30, distributions were visually inspected by histograms and Q-Q plots. Per age category, an independent-samples t-test (normality assumed) or Mann-Whitney test (normality violated) was conducted to compare PPA en PPB between elite and high-competitive swimmers. To interpret the scores, effect sizes (r of d, depending on normality) were calculated. An effect size of approximately 0.20 (d) or 0.10 (r) was considered small, 0.50 (d) or 0.30 (r) moderate and 0.80 (d) or 0.50 (r) large (Cohen, 1988). Statistical tests were executed for the age categories in which there were more than six observations in the elite performance group. For all tests, p <0.05 was set as significance. Results Figures 2 and 3 illustrate the performance progression in phase A (PPA) and phase B (PPB) respectively of talented male and female swimmers on the 100m freestyle from age 14 to 24 (males) and 12 to 22 (females). Within each age category, all swimmers performed within the corresponding performance benchmarks, however part of them reached the top (elite swimmers) and part of them did not reach the top (high-competitive swimmers). The average period of PPA was 252 ± 87 days and the average period of PPB was 102 ± 76 days. Except for age 14 in males, Mann-Whitney tests and independent sample t-tests showed no significant differences between elite and high-competitive swimmers in PPA. For males, we found significant differences in PPB between elite and high-competitive swimmers from age 15 till 24 (p <0.05). From age 15 onwards, male elite swimmers improved on average more in their swim performance than male high-competitive swimmers in the period between their first swim performance of the current season and their current season best performance. For females, we found significant differences in PPB between elite and high-competitive swimmers from age 13 till 22 (p <0.05). From age 13 onwards, female elite swimmers improved on average more in their swim performance than female high-competitive swimmers in the period between their first swim performance of the current season and their current season best performance. Corresponding test statistics are reported in Appendix D and E (males and females respectively).
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