This box and whisker plot shows how runners’ finish times change between the first and second halves of the 2024 Boston Marathon, broken down by age group. The chart displays percent change in split times, with positive values indicating a slower second half. It uses d3.scaleBand and d3.scaleLinear for axes, while box plot statistics are calculated manually from the data. Outliers are filtered by removing the most extreme 20% of values beyond the whiskers. The visualization is built with React and D3 v7, reading from a CSV of finisher data sourced from Kaggle.