Lane bias in elite-level swimming competition

Performance outcomes at the 2013 World Swimming Championship were previously shown to be biased depending on the swimmer’s lane assignment. The purpose of this study was to determine if this kind of bias was unique, and if not, if the bias was related to the temporary or permanent nature of the pool. The effect of lane on the average odd-length split minus the preceding even-length split in the 800- and 1500-m freestyle events, and on the relative change from qualifying to preliminary performance in the 50-m events, was determined for 16 other elite-level competitions. Depending on the swimmers’ direction, split times were on average 0.16 s slower or faster in at least one lane at each of the 16 competitions, and in 49% of all lanes analysed. In 5 competitions, swimmers were shown to be faster in a majority of lanes in one direction as compared to the other. Analysis of the 50-m events at these 5 competitions indicate that preliminary performances were between 0.5 and 0.9% slower or faster than qualifying times, which is consistent with the direction effect observed in the distance freestyle events. Further, lane biases occur more often in temporary pools (70% of lanes) than in permanent pools (35% of lanes), with water currents as the most plausible cause. The prevalence of lane bias at elite-level swimming competition highlights the need for the implementation of policies and procedures to prevent such bias from occurring again in the future.