How the Passenger Survey Data is validated
Once the interviews have been conducted there are a number of validations processes that are undertaken to ensure that the data is as clean as possible. These processes are outlined below.
The processes of validation of the Passenger Survey Database are undertaken at four stages.
Validation at Data Entry
The first stage of validation occurs at the Data Entry stage (when the completed questionnaires are input into the survey database). Both the Data Entry Clerk and the Data Entry programme have a part to play at this stage.
Firstly, the Data Entry Clerk manually assesses each response on the questionnaire to determine that the information being input is feasible.
Secondly, the Data Entry programme has a range of validations that trap coding and interviewing errors on many of the questions. Some examples of these validations are listed below.
If a Data Entry Clerk is unable to input a response because a particular code is not on the relevant reference table or if they have a specific query with that response then they are able to "flag" that question. This involves inputting a temporary code that is then subsequently revised by Head Office.
Each flag is assessed in Head Office and temporary codes are replaced with the correct code. Where necessary, new codes are added to reference tables.
Validation post Data Entry
The Survey database is also subject to a series of validation checks prior to the weighting process to ensure the integrity of various aspects of the data. This is an ongoing process throughout the year minimising the number of records which have to be discarded as a result of missing, incorrect or ambiguous data.
Manual adjustments may be necessary in order to enable the weighting process to run correctly – for example, harmonisation of codeshare flight numbers.
In addition to the above measures, the data is subject to ongoing Quality Control inspections to ensure the integrity is the highest possible. This covers all aspects of the data, including the final weights calculated.