Process of measuring in clinical medicine--implications of different definitions in clinical therapeutic studies.

Often, the decision whether a patient can be considered as healthy or ill is very difficult and depends on measurements and the interpretation of the results. Therefore, it is necessary to build and establish devices that base on certain pre-considerations (who should assess the data, when and how should be measured). Additionally, these devices have to be valid, reliable and responsive. According to the literature we came to the conclusion that no uniform definition of what is 'healthy' exists. Referring to mathematical considerations we show an approach to solve this problem especially when the device is a scale. Based on the quality of the scale and of certain pre-considerations normal ranges can be established that will help to distinguish whether patients are 'healthy' or 'ill'. In this short review we discuss the problem of the establishment of a cut-off level on the basis of devices and we try to point out a solution to solve the arising problems.