Question

For the time being, the air traffic control system in the United States is run by the federal government. Some people would like to change this, arguing that the air traffic control system should be part of the private sector. Among the arguments given for the privatization of air traffic control is that flight delays are much too common in the United States. A first step in deciding if, indeed, delays in the U.S. are too common might be to compare flight delay information from the U.S. and other nations. Suppose that you have in front of you information from several samples of flights over the past six weeks. Each sample is composed of domestic flights for a certain country. (One of the samples is composed of flights within the U.S., one of the samples is composed of flights within Canada, and so on.) The information recorded for each flight is the time (in minutes) that the plane was late to the arrival gate. (If the plane was early, then the time recorded is negative.) Based on this information, you perform a one-way, independent-samples ANOVA test of the hypothesis that there are no differences in the mean flight delay times among the several countries. The results of this ANOVA test are summarized in the ANOVA table below. Complete the missing cell in the ANOVA table (round your answer to at least two decimal places), and then answer the questions Source of Variation Degrees of Freedom Sum of Squares Mean Square Fstatistic Between groups 2 545.55 272.78 0 Error (Within Groups) 712 76140.6 106.94 Total 714 76686.15 How many countries total were studied? 0

Answer 1

1. df for total = 714 = n-1 so n = df +1 = 714 + 1 = 715 countries.

2. Unbiased estimate of this population variance is MSE = Mean square error = 106.94

3. For alpha = 0.01

and numerator df = 2, denomiator df = 712

We have F_(2,712) = Critical value = 4.635.

Now, F-calculated = MST/MSE = 272.78/106.94 = 2.551

4. No

Since, F_cal $\ngtr$ F_critical, we fail to reject Ho or can say that population variances of flight delay times are equal for each country studied.

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