Standard error of average reaction time

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A lab measures a subject's reaction time across n = 25 trials. The sample standard deviation of the times is s = 45 milliseconds. What is the standard error of the average reaction time?

Accepted Answer

Reaction times bounce around from trial to trial (spread about 45 ms), but the average of many trials is a much cleaner estimate of the subject's typical speed. The standard error of the mean measures how precise that average is. Divide the single-trial spread by the square root of the number of trials: 	ext{SE} = \frac{s}{\sqrt{n}} = \frac{45}{\sqrt{25}} = \frac{45}{5} = 9 	ext{ ms}. The average is pinned down to about 9 ms, five times tighter than the 45 ms scatter of individual trials, because \sqrt{25} = 5. Takeaway. Standard error of the mean = s/\sqrt{n}: with 25 trials the average is…

Standard error of average reaction time

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