[Methodological aspects of use of scales as measurement instruments in epidemiological studies].

Quality of life and health status measurement in epidemiological studies requires high level approach. It concerns not only the matter of choice or development of measurement tools; it requires also consciousness of the consequences, which may follow mistakes made during their development. Development of new measurement tool by means of adaptation of tool used in another country also may be touched by the risk of committing some mistakes, which may be followed by serious consequences including problems with interpretation of obtained data. This paper presents examples of mistakes made during development of questionnaires and some guidelines, which let to avoid the most serious mistakes.