Primary variables

Secondary variables

Coding principles

Time

Year

1—2015, 2—2016, 3—2017, 4—2018, 5—2019

Season*

1—Winter-Spring, 2—Summer-Autumn

Quarter

1—1st quarter, 2—2nd quarter, 3—3rd quarter, 4—4th quarter

Monthly

1—January, 2—February, 3—March, 4—April, 5—May, 6—June, 7—July, 8—August, 9—September, 10—October, 11—November, 12—December

Complaint against

1—Domestic airline, 2—Foreign airline.

Type of complaint

1—Flight problems, 2—Fare problems, 3—Baggage problems, 4—Check-in problems, 5—Airline problems, 6—Over-selling problems, 7—Special services, 8—Cargo problems, 9—Other problems