A proposed method to determine confidence in a construction schedule

Abstract

Construction is uncertain, and so too are the schedules used to manage them. Most view uncertainty as an exercise of probability theory. The flaw in this approach is the presumption that all uncertainty is the result of natural variability, even when the source of uncertainty is non-specificity, uncertainty due to judgment, or vagueness. How can a project manager recognize the non-traditional types of uncertainties that might be present in a construction schedule? How does one quantify the different types of uncertainties in a schedule? Researchers have offered new scheduling techniques recognizing that epistemic uncertainties exist, but none have attempted to quantify in a single number all the uncertainties that might be present. Through a series of thought experiments, techniques are offered here to allow one to not only recognize various uncertainties in a schedule but also how to individually quantify them. To verify the issues that plague construction and cause delays, interviews were conducted with commercial contractors to verify typical problem areas. A technique using non-square matrices and singular value decomposition was developed to combine all the uncertainties present and assign a single number, the Total Uncertainty, to the schedule. Two approaches were tested, one that examined each activity on the schedule's critical path, and the other that looked at the project as a whole. Both methods were tested at the boundary conditions of zero and maximum uncertainty with satisfying results. By itself, Total Uncertainty does not provide added value, however relative uncertainty does. By calculating maximum uncertainty and actual uncertainty, it is possible to calculate confidence. These techniques offer a project manager a tool for determining the "goodness", though not necessarily the accuracy, of his construction schedule, and the confidence one should have as a result.