When the data is collected via a questionnaire, a questionnaire design phase is needed. It may entail a preliminary qualitative step, to identify topics of interest or the vocabulary used by the target population. The questionnaire design should ideally be followed by a validation phase, with expert checks, cognitive testing and/or a pilot phase.
Good practices in questionnaire design include carefully structuring and wording the introduction, questions, answers and conclusion. Participants should be able to understand the question, retrieve and formulate the answer, and communicate it. This applies equally to closed questions (with a list of possible answers) and open questions (allowing participants to answer in their own words).
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