Modeling of Identifying Mediator Effects between Project Delivery Systems and Cost Performance

This paper addresses the problem of explaining the reason for mixed assessment results in comparing cost performance of project delivery systems (PDS). In particular, we focus on mediator effects for the explanation that would traditionally not be handled by project performance evaluation disciplines. Previous studies revealed that two kinds of disciplines deal with change orders from different points of view. Evaluating PDS by project owners uses change order as a cost performance metric, whereas contractors consider it as a method to increase project cost for their own profit. A Path Analysis model was established by integrating these viewpoints to explain the discrepancy in assessment of PDS. It describes the process how PDS impact on change orders. For the path model, 234 public sector projects completed between 1998 and 2013 in Korea were collected and analyzed. The dataset consists of both Design-Build and Design-Bid-Build projects which are the most prevalent delivery systems. While examining the total effect of PDS on cost performance using the path analysis, mediator effects were significant in building construction project type. This study fills the gap between the successful performance result and the failed adoption of PDS using causal relationship as explanation. The intervention of procurement methods between PDS and their cost performance may provide the clue that project decision makers should consider mediator effects and project characteristics when they select and assess PDS.