The methodology of the development of knowledge bases for expert syste
ms is based on questioning of human experts. Until now, very little at
tention has been paid to the question of the consistency and accuracy
of the expert's estimations. This is a subject of great importance, es
pecially in areas requiring the estimation of probability events. In t
he research partially presented in the paper, a multistage methodology
was developed to elicit knowledge requiring subjective judgement. The
paper discusses an empirical application in the field of medical diag
nosis, and includes the results and conclusions drawn from it.