A description of the sampling methodologies used on the Departing Passenger Surveys
CAA surveys generally operate for twelve month periods with anywhere from 3,000 to 70,000 interviews being achieved, depending on airport size. The surveys usually follow a stratified sampling design (stratified by carrier, route and quarter), with interviews taking place in the gaterooms. The interviews are then weighted to actual traffic levels. (Less often, a random sample is obtained by interviewing at points in the lounge - in this instance a further level of weighting is required to account for the sampling proportion obtained during the shift).
Surveys usually run on an annual basis, with shifts spread as evenly as practical throughout the year. A record of the flights sampled is regularly monitored to ensure that where possible all routes, and in most cases all flight numbers, are covered regularly.
Departing passengers are selected for interview using a strict sampling system. Interviews are weighted to the two-way passenger flow, under the assumption that over the period, departing and arriving passengers will show the same characteristics. Information is collected from passengers by a skilled interviewing fieldforce.
An interview usually lasts 5 - 7 minutes, and involves around 30 questions being asked. All passengers are eligible, apart from children under two years of age.
It is assumed that passengers who are chosen for interview, but are unwilling or unable to respond (e.g. because of time constraints) have the same characteristics as those who are successfully interviewed. Thus no adjustments are made for non-response, either by item or by questionnaire.
The notes below outline the sampling methodology that is used when interviewing in the gateroom. This method can be used irrespective of the number of team members present and ensures that a random selection of passengers are selected for interview.