Measurement is an essential activity in medical science and due to the
subjective nature of the results that are being measured, it is
increasingly necessary to have valid, reproducible and reliable methods.
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.
Before any data collection, a translation of the questionnaire is
needed. Psychometry involves the application of statistical techniques
to test the measurement properties of an instrument. There are several
measures to evaluate an instrument, the main ones being: classical test
theory and modern test theory. Regarding the classical test theory, the
key psychometric characteristics are: scale structure, accuracy
(validity), precision (reliability) and responsiveness. Modern test
theory models are techniques to assess the psychometric characteristics
of an instrument, focused on the dimensionality of the questionnaire.
Responsiveness, validity and precision are interlinked. However, each
one is important, acting independently in the assessment of the
psychometric characteristics of the instruments.