Duration of daylight in western Pennsylvania. What area of the United States has the least amount of daylight, on average?

Having grown up in western Pennsylvania, co-author Sincich wonders if it is his hometown of Sharon, PA. Data on the number of minutes of daylight per day in Sharon, PA, for 12 randomly selected days (one each month) in a recent year were obtained from the Naval Oceanography Portal Web site (aa.usno.navy.mil/USNO/astronomicalapplications/

data-services). The data are listed in the table.

Descriptive statistics and a 95% confidence interval for the mean are produced in the SPSS printout in the next column.

a. Locate the confidence interval on the printout and give the value of the confidence coefficient.

b. Use the descriptive statistics on the printout to calculate the 95% confidence interval. Be sure your answer agrees with the interval shown on the printout.

c. Practically interpret the confidence interval.

d. Comment on the method of sampling. Do you think the sample is representative of the target population?

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