SUBJECTIVE AND INTERACTIVE DURATION ESTIMATION

Scheduling of construction projects with an uncertainty content requir es that the scheduler's subjective knowledge of various factors that m ight influence the duration of the activities comprising the project i s incorporated. Depending on the participating factors and their signi ficance, a different duration outcome is often observed for each activ ity. To include this uncertainty in the schedule, a statistical distri bution is frequently used. This paper presents a system based on the p remise that part of the information available, when duration distribut ion is being estimated, exists in a subjective form. We present an aut omated system that requires the modeler to specify the activity's mini mum and maximum times and a set of linguistic descriptors of the exter nal factors that are suspect of influencing the duration. The lower an d upper end point estimates are often available from familiarity with the technology used, physical and logical constraints, or a combinatio n of these situations. The subjective information collected by the mod eler is modeled as fuzzy parameters and is quantified using fuzzy set theory. The result of the fuzzy set analysis is a sample of activity d urations from the underlying distribution, which is then used to chara cterize the first two moments of that distribution. Since earlier rese arch has shown that the beta distribution provides an adequate represe ntation for construction durations, the end points specified by the us er and the two moments resulting from the fuzzy set analysis are used to fit a beta distribution. The system then allows the user to visuall y assess the quality of the fit and modify the shape of the beta densi ty using the visual interactive beta estimation system. The paper also presents a practical construction scheduling application to demonstra te the use of the developed system.