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ivity of medical science. In order to acquire data about people, objects, and events proper data collection tools need to be designed which can measure things of scientific interest. Questionnaire is one of the most important techniques to collect data. It is a common experience that many studies focus on similar objective and theme but have entirely different questionnaires. It is extremely important for a researcher to know the importance of a proper questionnaire and whether it measures what it is intended to measure. Composing of a questionnaire is always much more complex than expected and great attention is required to its flow, format and length. Making an individual question is a tedious task and validating this questionnaire is another challenge which at times is over looked. Consideration should be given accordingly on whether the questionnaire will measure quantitative or qualitative data, and what would be its mode of administration.
The aim of this paper is to give a basic introduction and broad overview to the readers on questionnaires for epidemiological studies.
Questionnaire Development:
A questionnaire is a tool to obtain information from respondents. It is an efficient way to collect data, the investigator should be certain on what is required and how to measure the variables of interest. As a first step it is always recommended to do a literature search on previously used validated questionnaires that can be administered in similar settings and capture variables that are of interest according to the study hypothesis. These questionnaires do not need to be tested for reliability and results can be compared for different studies and also combined for meta- analysis. However one needs to make sure that the mode of administration should be similar to the original questionnaire.1
If a new questionnaire is to be developed, it should be pilot tested and validated in order to evaluate if it is measuring what it supposed to measure and is it doing it reliably. Wording of questions is very critical and should take into consideration; appropriateness of the content, level of sophistication of language, type and form, sequence and how is data sought from the respondents. During questionnaire development its mode of
administration should be kept in mind, whether it will be self- administered or interview based and its design and flow should be planned accordingly.2 See Table on common problems in questionnaire.
The language of questionnaires should be at the level of understanding of the participants. It is essential to word the questions in a way that they can easily be understood by participant and should be according to their educational level and culture. 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.3
Translation of a questionnaire is essential if an instrument is not available in a language understood by the target population. The initial stage of translation is a source language questionnaire, from which translation in required language is done. Translation is not a mechanical work and should not be done on word to word bases across languages. It is important to understand the local context, specific issues and cultural meanings which language carries. Translation should not only be concerned with translating meanings, but it should also understand how the language is tied to local realities and literary forms. The term back translation is highly recommended in questionnaires related to health surveys. Back translation helps in evaluating the quality of the translation. The source language is translated in another language and again translated back into the source language. Translation back to the source language is done by another translator who is unaware of the source language version.4
Validity:
Validity is the degree to which an assessment measures what it is supposed to measure. Validity is a complex topic and it is beyond the scope of this paper to explain it in detail, however to make the readers acquainted we have described it briefly. Essentially there are three types of validity i) content validity, ii) criterion- related validity, and iii) construct validity.5 A questionnaire undergoes a validation procedure to make sure that it accurately measures what it aims to do, regardless of the responder. Valid questionnaire helps to collect better quality data with high comparability which reduces the effort and increase the credibility of data. A valid questionnaires must have