Scenario: We have additional flight data in the data table Airline delays 3, which contains data for every United Airlines flight departing Chicago’s O’Hare International Airport from March 8 through March 14, 2009. Canceled flights have been dropped from the table. Our goal is to analyze the departure delay times, expressed in minutes.

a. Assume this is an SRS. Have we satisfied the conditions for inference about the population of United flights?

b. “Departure Delay” refers to the time difference between the scheduled departure and the time when the aircraft’s door is closed and the plane pulls away from the gate. Develop a 95% confidence interval for the mean departure delay DepDelay, and interpret the interval.

c. Sometimes there can be an additional delay between departure from the gate and the start of the flight. “Wheels off time” refers to the moment when the aircraft leaves the ground. Develop a 95% confidence interval for the mean time between scheduled departure and wheels-off

(SchedDeptoWheelsOff). Report and interpret this interval.

d. Now use a matched-pairs approach to estimate (with 95% confidence) the mean difference between departure delay and wheels off delay. Explain what your interval tells you.