In designing an experiment, a psychologist is willing to assume that the underlying distribution for the time to learn a list of words is approximately normal with a standard deviation of 40 seconds. He wants to be 95% sure that the maximum error of his estimate of the mean is at most 10 seconds. What sample size should he use?

Question

In designing an experiment, a psychologist is willing to assume that the underlying distribution for the time to learn a list of words is approximately normal with a standard deviation of 40 seconds.  He wants to be 95% sure that the maximum error of his estimate of the mean is at most 10 seconds.  What sample size should he use?

PsyDAG · Answer

95% = mean ± 1.96 SEm SEm = SD/√n 10 ≥ 1.96 (40/√n) Solve for n.