A mathematically elaborated modeling method alone cannot develop useful models of large-scale systems that involve human activities. What is needed as input to the model-building process, besides measurement data, is the knowledge of experts in relevant fields. The problem is, then, what types of knowledge should or can be included in the modeling process and, more important, how do we manage them. The interactive method of data handling (IMDH) presented in this paper develops linear models of complex systems through recursive interaction with the computer, systematically introducing the expert's knowledge about the structure of the underlying system. It should be emphasized that the more one repeats dialogues with the computer, the more effectively knowledge can be used to develop and refine the model
