Introduction
Measurement is an essential activity in medical science. To acquire data on people and events, and to measure the intended scientific interest, the appropriate data collection tools need to be designed. Questionnaire is one of the most crucial 1.
Due to the subjective nature of the results that are being measured, for example, quality of life (QoL) impact or disease severity, it is increasingly necessary to have valid, reproducible and reliable methods2. There are several instruments (indexes, questionnaires, scales) which can measure a certain characteristic in health. In the last decade, the impact and use of these instruments has increased 3 and their importance is increasingly emphasized. It is important to know the opinion of patients and what they feel daily, and also their opinion on the care provided by health professionals and the service they use, in order to create treatment goals or improve the care provided.
The composition of a questionnaire is always much more complex than expected and great attention is needed to its flow, shape and length. Accordingly, it should be assessed whether the questionnaire will measure quantitative or qualitative data, and which method of administration 1.
There is no guidelines simply focus on the validation of questionnaires. There are some reviews or task forces. Nevertheless, looking at some validation studies, there are different methods or techniques to develop it, which may cause some confusion. The aim of this review is to synthetize some of these information, to be used as a simple guide for researchers and/or clinicians facing the need to validate a questionnaire.