Figure 7.12: Figure 7.9 95% Confidence Interval for the Difference Between Population Means for the Reaction-Time Study Imagine a race in which a person representing the average American crosses the finish line first, followed by a person representing the average adult with ADHD. How much slower is the average adult with ADHD? The confidence interval says that the average adult with ADHD probably trails the average American by anywhere from 15.51 msec to 24.49 msec, but it doesn’t specify where in that range the average adult with ADHD is.