Sportsbooks set the handicap lines for horses in a race by employing a combination of data analysis, expert evaluation, and market dynamics. Initially, they assess a horse's past performances, including speed figures, recent race results, and how well the horse has fared against similar competition. Information about the jockeys, trainers, and any relevant changes, such as equipment alterations or class adjustments, are also taken into account. Once a preliminary assessment is made, oddsmakers then adjust the lines based on betting patterns and public sentiment, which can lead to shifts in the odds as money is placed on various horses.