UNCERTAINTY, SUBJECTIVITY, EXPERIENCE - A COMPARATIVE PILOT-STUDY

Mean tendencies and variances of ad hoc mean estimates (held estimates ) of some engineering geological parameters were compared to statistic ally obtained reference values. The latter correspond to the ''best'' estimates in the sense of approximating so-called reality (Einstein an d Baecher, 1982. Probabilistic and statistical methods in engineering geology. Problem statement and introduction to solution. Rock Mech., S uppl. 12: 47-61; Einstein and Baecher, 1983. Probabilistic and statist ical methods in engineering geology. Specific methods and examples, Pa rt I: Exploration. Rock Mech. Rock Eng., 16: 39-72). The study was car ried out by means of a demoscopic field study on 43 engineering geolog ists. ''Professional experience'' was examined by comparing the estima tion results of two trial groups, one consisting of people with severa l years of professional experience, the other one consisting of univer sity students. The biases of the ad hoc estimates due to subjectivity and the limitation of working time at the selected reference outcrops follow statistically describable trends and thus can be analyzed by un ivariate and multivariate methods. Some geological and psychological h ypotheses concerning the mean estimation trends, correlations and disc riminations are postulated. Implications on commonly used held estimat ion methods are discussed.