24 Chapter 2 Table 2. Total number of swimmers (N = 3,146) and observations (N = 23,010) for each performance group for the analysis on swim performance (rSBT). Males Females Individuals Observations Individuals Observations Top-elite 29 274 57 504 Elite 62 582 218 1,734 Sub-elite 394 3,265 378 2,786 High-competitive 820 6,059 1,188 7,806 Total 1,305 10,180 1,841 12,830 Defining first entry ages For top-elite swimmers only, we determined the first entry age of each performance level. The first entry age is the minimum age at which a swimmer for the first time achieved a higher performance level (e.g. performance level transition from sub-elite level to elite level). First entry ages for skipped performance levels (e.g. a performance level transition from sub-elite level to top-elite level) were not reported. Statistical analysis All data were analyzed for male and female swimmers separately using IBM SPSS Statistics 24 and R. Mean scores and standard deviations were calculated for swim performance (rSBT) for the four performance groups per age category. Per age category, a one-way independent analysis of variance (ANOVA) was used to examine group differences based on rSBT with performance group as independent variable. Planned contrasts were performed to determine differences between top-elite swimmers and swimmers of other performance groups per age category. A frequency analysis with first entry age as variable was executed for top-elite swimmers only. Mean scores and frequency distribution tables of first entry age were produced for the four performance levels (high-competitive level, sub-elite level, elite level and top-elite level). Statistical tests were executed for the age categories in which there were more than two observations in the top-elite performance group. For all tests, p <0.05 was set as significance. Results Differences in swim performance between top-elite swimmers and other performance groups Figure 1 illustrates the performance development of male and female swimmers on the 100m freestyle from age 12 to 26 (males) and 12 to 24 (females) specified for each of the four performance groups.
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