You desire to do a study of ax murderers in American prisons. A preliminary stud

Question

You desire to do a 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. What exactly does this confidence interval tell me? (Be scientific, not sociological.) Also, please demonstrate how this formula is done in Excel (what is required to input in what fields, etc.), as I am not sure how to do this.

Explanation / Answer

sample size, n = 156
mean, = 80,

standard deviation, = 24.

standard error, e = /n = 24/156 = 1.922

at 95% confidence for a two tail distribution, z = 1.96 (from z table)

95% confidence interval on the mean IQ of ax murderers = ± (z*e)

=80 ± (1.96*1.922)

= (76.23288, 83.76712)

this confidence interval tells that mean IQ of ax murderers lies between the interval (76.23288, 83.76712)

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