## Practice Problems: Confidence Intervals

A sample of students from an introductory psychology class were polled regarding the number of hours they spent studying for the last exam. All students anonymously submitted the number of hours on a 3 by 5 card. There were 24 individuals in the one section of the course polled. The data was used to make inferences regarding the other students taking the course. There data are below:

 4.5 22 7 14.5 9 9 3.5 8 11 7.5 18 20 7.5 9 10.5 15 19 2.5 5 9 8.5 14 20 8

Compute a 95 percent confidence interval. What does this tell us?

Mean = 10.92
Standard Deviation = 5.598265777
Standard Error = 1.167319108

t = 2.069

Confidence Interval at 95 percent: 8.50 < population mean < 13.33

We are 95 percent sure that the actual population mean for the number of hours introductory psychology students studied for the last exam was somewhere between 8.5 hours and 13.33 hours. There is a 5 percent chance that the population mean does not lie within that interval.

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