Prior to weighting the survey records, various validation exercises are carried out to identify miscoding of flight
numbers, destinations and routeings. Where possible these are corrected and the record retained. See the survey validation page for more information.
The survey design is stratified by carrier, route and quarter for scheduled traffic, and route and quarter only for
charter traffic. There may be multiple flight numbers within these stratification cells, but it is possible that there
will only be one.
As interviews are generally conducted in the gateroom it is possible to target specific flight numbers. For
scheduled flights, the intention is to cover as wide a range of flight numbers and routes as possible during the
quarter. For charter flights, the focus is on sampling the route rather than individual flight numbers on the
The interviews are weighted firstly by matching the total airport passenger numbers to the stratification cells, and
then by spreading these totals across the interviews achieved in each cell. Multi-sector routes are treated slightly
differently to single sector routes to allow for the multiple destinations on a given flight number.
Only departing passengers are interviewed. In order to weight the interviews achieved such that they represent all
the airport passengers, the departing passenger totals on each flight number are scaled up to represent both departing
and arriving passengers. This is done with a constant scaling factor across the carrier-route in each month, which is
then applied to each departing flight number within that carrier-route, such that the total of the scaled up departing
flights on the carrier-route agrees to the total passengers travelling on the carrier-route. The various airport
authorities provide uplift/discharge figures for each month.
If no interviews have been obtained on a given scheduled flight number, the stratification cell is extended to
consider other flight numbers by the carrier to the same destination in the quarter.
If no interviews are recorded in the stratification cell (or extended cell) in the quarter of the flight departure,
the search is extended to other quarters. If no interviews at all have been obtained in the year on the carrier-route
(or just the route in the case of charter traffic), the population has to be dropped from the survey weights.
Determine the scaling factor for departing flights by the BA to CDG in each month in quarter 2.
Use the scaling factors to gross up the passengers on departing flight BA1 in each month.
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