Steps in validating a survey instrument
A questionnaire undergoes a validation procedure to make sure that it accurately measures what it aims to do, regardless of the responder.
Consideration should be given accordingly on whether the questionnaire will measure quantitative or qualitative data, and what would be its mode of administration.
If the questions are interpreted differently by the participants it will result in wrong answers and responses will thus be biased.
Reading ease of a questionnaire can be assessed by Flesch reading ease score.
A questionnaire could be structured, in which all the participants are asked same questions in the same way, this is usually interview based questionnaire format.
The other type is unstructured questionnaire and questions may vary at the discretion of the interviewer.