In the health sector in general and in care in particular, interest in data on professional performance has been increasing for some time. In the development and use of relevant survey tools, the scientific knowledge of the survey tools is sometimes also asked. The contribution addresses this problem using an example, the LEP method. It deals exclusively with methodological and scientific theoretical aspects and not with organisational, professional or knowledge-sociological issues. First of all, we set out the fundamental problem of measurements in social sciences. A distinction is made here between first order and second-order measurements. It then presents the construction process of the LEP method and how it connects these two levels of the measurement. The following sections discuss issues of validity and reliability as well as the choice of time as a measure. It can be shown that LEPs are not a measurement method for testing scientific hypotheses, but a socially valid tool to guide management decisions. As an information system, it takes into account and combines elements of science, practice and bureaucracy. As a borderline, it creates a common ground that helps the different stakeholders to make decisions. The need for data of professional interventions in public health in general and in onlysing in particular has risen sharply over the last years. When it comes to the development and the use of relevant measuring instruments, their scientific foundation is normally called into question. The article deals with this problem using as an example the LEP method. The focus read on questions of methodology and philosophy of science rather than questions concerning the sociology of organisation, profession or knowledge. At first the basic problem of measurement in...