An experimental study of individual subjective effort estimations and combinations of the estimates

The required effort of a task can be estimated subjectively in interviews with experts in an organization in different ways. Interview techniques dealing with which type of questions to ask are evaluated and techniques for combining estimates from individuals into one estimate are compared in an experiment. The result shows that the interview technique is not as important as the combination technique. The estimate which is best with respect to mean value and standard deviation of the effort is based on an equal weighting of all individual estimates. The experiment is performed within the Personal Software Process (PSP).