Learning objectives: You will learn how questionnaires can be used as a tool for collection of data. The section introduces you to essential criteria and methods for developing a valid questionnaire. Read the resource text below.
Questionnaires are a commonly used tool in epidemiological studies. They may be used as the sole instrument for the collection of study data, such as in a cross-sectional design, or in combination with other instruments of data collection. The degree to which a questionnaire produces data that are relevant and valid to a study's goals and objectives will depend on how well the questionnaire is designed, how well questions are constructed, and how well the questionnaire is administered. A valid questionnaire measures what it claims to measure. For example, a self-completed questionnaire that seeks to measure people's food intake may be invalid because it measures what they say they have eaten, not what they have actually eaten .
Basic guidelines for constructing a valid questionnaire
Careful consideration of a study's objectives and aims in the design of a questionnaire are essential if it is to yield responses that are both valid and reliable.
Types of questions
Questionnaire items may be open or closed ended and be presented in various formats.
Closed questions are questions which limit the response to a specified list of possible answers. The use of closed questions offers a number of advantages to the researcher, including providing a set of standard responses that enable researchers to produce aggregated data quickly. However, the range of possible answers is set by the researchers not respondents, and therefore the richness of potential responses is lower. In addition, if a closed question fails to include all potential responses then important information relating to the overall study objectives may be omitted, leading to biased results. Where appropriate, closed questions should include an opened ended question for 'Other' and an option for 'Don't Know'. In contrast, open questions allow the respondent to answer freely. However, if opened ended questions are used, then the methods for analysing these responses should be considered during the design of the questionnaire .
Piloting the questionnaire among a representative sample of the target population in the same way that it will be administered in the main study is essential and will help identify potential problems with the design or layout of the questionnaire. Piloting will:
- Help determine whether questions are ambiguous and allow questions to be rephrased.
- Check that instructions are clear and easy to follow.
- Test whether the questionnaire can be administered in a reasonable amount of time.
- Enable investigators to eliminate questions that do not produce usable data.
- Assess whether each question provides an adequate range of responses.
- Enable investigators to rephrase questions or replace existing scales where appropriate.
- Determine whether responses can be interpreted in terms of the objectives of the study.
- Determine whether the questionnaire is culturally acceptable to study participants.
Maximising response rates
- Notify participants in advance with a letter of introduction that outlines the purpose and importance of the study.
- Include clear instructions of how to complete the questionnaire.
- Clear and simple layout.
- Questions should be clear and concise and avoid the use of technical jargon and long, leading or negative questions.
- Inclusion of a stamped, addressed envelope if conducting a postal survey.
- Ensure anonymity where possible.
- Highlight the public health importance.
- Follow-up of non-responders by telephone or letter.
- Use of a researcher who is available to answer questions.
- Collection of questionnaires where feasible by the researcher.
1. Boynton, PM, Selecting, designing, and developing your questionnaire, BMJ 2004;328:1312-1315. 2. Boynton, PM, Administering, analysing, and reporting your questionnaire, BMJ 2004;328:1372-1375.