Definition · Plain-language
Questionnaire
A questionnaire is a research instrument made up of a standardised set of questions used to collect data from respondents in a consistent, comparable way.
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A standardised data-collection instrument
A questionnaire is a structured list of questions presented to every respondent in the same wording and order, so that the answers can be compared and aggregated. That standardisation is its defining strength: because each person faces an identical instrument, differences in their answers can be attributed to the respondents rather than to how they were asked. Questionnaires can be self-administered (on paper or online) or delivered by an interviewer, and they are central to survey research across the social sciences, health, and market research.
Open-ended versus closed-ended questions
Closed-ended questions offer respondents a fixed set of options — yes/no, multiple choice, or a Likert scale from "strongly disagree" to "strongly agree". They produce quantitative data that is quick to code and analyse, but they constrain answers to the options the researcher imagined. Open-ended questions invite free-text responses, yielding rich, qualitative detail and unexpected insights, at the cost of being harder and slower to analyse and code consistently. Many questionnaires combine both: closed questions for the bulk of measurement and a few open ones to capture nuance.
Designing good questions
Question wording strongly shapes the answers, so careful design is essential. Avoid leading questions that nudge respondents toward a particular reply, and double-barrelled questions that ask about two things at once ("Was the service fast and friendly?"), since respondents cannot answer cleanly. Keep language plain, define ambiguous terms, and offer balanced response options. Crucially, pilot the questionnaire on a small group first: piloting surfaces confusing items, missing options, and ordering effects before they contaminate the main dataset.
Key facts
At a glance
- Definition: a standardised set of questions used as a data-collection instrument
- Question types: closed-ended (fixed options) and open-ended (free text)
- Closed gives: quantitative data, easy to code, limited by preset options
- Open gives: qualitative detail, richer but harder to analyse
- Design rules: avoid leading and double-barrelled items; always pilot first
- Not a synonym for: a survey — the questionnaire is the instrument, the survey is the study
Common misconceptions
What people often get wrong
Often heard: A questionnaire and a survey are the same thing.
Actually: They are not. A questionnaire is the instrument — the set of questions — while a survey is the wider research process of designing, distributing, collecting and analysing responses, of which the questionnaire is one part.
Often heard: Open-ended questions always give better data than closed-ended ones.
Actually: Neither is universally better. Closed questions yield quantitative, easily compared data; open questions give qualitative depth. The right choice depends on the research aim, and many questionnaires combine both.
Often heard: Any clearly written question is good enough without testing.
Actually: Wording effects are subtle. Leading, double-barrelled or ambiguous items distort results, so a pilot study on a small sample is needed to catch problems before full data collection.
