Question

Travel Data 10. Using your travel data: a. Develop a 95% confidence interval for your mean time to work (lunch) using time in minutes. b. What assumption is necessary for you to complete part (a)? Do you feel this assumption is valid?

Answer 1

The output is:

Descriptives Std. Error 328 Time Mean 95% Confidence interval for Mean Lower Bound Upper Bound Statistic 9.57 8.90 10.24 9.44 9.00 5% Trimmed Mean Median Variance 3.220 1.794 Std. Deviation Minimum Maximum Range Interquartile Range Skewness Kurtosis 1.131 1.669 .427 .833

(a) The 95% confidence interval is between 8.90 and 10.24.

(b) The assumptions for a 95% confidence interval are:

(i) The data must be sampled randomly.

(ii) The sample values must be independent of each other. This means that the occurrence of one event has no influence on the next event.

(iii) When the sample is drawn without replacement (usually the case), the sample size, n, should be no more than 10% of the population.

(iv) The sample size must be sufficiently large. In general, a sample size of 30 is considered sufficient.

Thus, the assumption is valid for the problem.

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