A method for determining an electrical property of interest of material(s) in a target region confined by a boundary surface comprises receiving measured values of a measurable electrical quantity; providing simulated values of the measurable electrical quantity for an initial approximation of the electrical property conditions; determining an objective function comprising observation difference between the measured and the simulated values as well a prior model, and determining an adjusted approximation; and providing, on the basis of the adjusted approximation, an estimation of the electrical property of interest. Simulated statistics of a position deviation in the observations is provided, caused by a difference of an effective position of the measurement probe from a predetermined reference position; and by providing the observation model to define the observations of the measurable electrical quantity to correspond to measurements made with the measurement probe in the reference position.