Last update:
10-Jan-2013

In epidemiological studies the use of appropriate questionnaires for essential data collection is fundamental for achieving validity and reliability. The researchers must firstly determine with clarity their research hypothesis, in order to create and use the appropriate questionnaire in an effective way. The questionnaire items must be relevant to the research hypothesis of the study. In order to achieve this it is necessary to conduct a systematic literature review, on the basis of which the researchers can design their study in an appropriate way with use of the appropriate questionnaire. After creation of a new questionnaire or the choice an instrument already in use, a pilot study must be conducted with a relatively small number of participants (roughly 30−50), in order to make a preliminary estimation of the validity and reliability of the questionnaire and to correct as far as possible its errors and failures. The first part of each questionnaire should be a cover letter, which is very important since it is the first contact of the candidate participants with the study and the questionnaire that they are required to answer. The cover letter should be brief, explicit and comprehensive, encouraging the reader to complete the questionnaire and participate in the study. Questionnaires usually consist of "closed" and or "open" questions. "Open" questions have no predefined answers, but allow the participants every possible response. Concerning "closed" questions, the participants have to choose between answers predefined by the researchers. "Closed" questions are used mainly in quantitative research, while "open" questions are used mainly in qualitative research. The format of a questionnaire is very important in order for it to be answered appropriately by candidate participants. A study questionnaire in a study should ideally be short, comprehensive and explicit, in order to increase the response rate of the participants.

Key words: "Closed" question, Likert scale, "Open" question, Questionnaire.