[Some methodological issues about measurements in health].

Measurement process is a part of everyday work of health professionals. Technological advances have created precise and sensitive instruments whose results are highly accurate and cast little doubt. However, health care has diversified, becoming a multidimensional and complex task. This means that new aspects, that are difficult to measure, must be addressed, such as health perception by patients or cost usefulness ratios of health actions. Therefore, clinicians and researchers must have a good perception of the quality of measures that they use in their daily work, to make the correct diagnostic, therapeutic or prognostic decisions. This article explores the operational concepts that help in the development and assessment of measuring instruments in terms of validity and truthfulness.