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Question: You desire to study of ax murderers in American prisons. A preliminary study reveals that the mean IQ of a random

sample of 156 ax murderers is 80, with a standard deviation of 24. Perform a 95% confidence interval on the mean IQ of

ax murderers, and provide the interval.


Answer: n=156, x-bar=80, standard deviation σ =24, %=95 Standard error, SE= σ/√n =24/√156 =24/12.49=1.92 For 95% z-score = 1.96 So, the width of the confidence interval=z*SE = 1.96*1.92=3.7632 Lower Limit=x-bar - width= 80-3.7632= 76.2368 Upper Limit=x-bar + width= 80+3.7632= 83.7632 So, the confidence intervals is [76.2368, 83.7632] (Ans.)  Edit

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