Cost Performance Comparison of Design-Build and Design-Bid-Build for Building and Civil Projects Using Mediation Analysis

This study analyzes the cost performance of design-build (DB) and design-bid-build (DBB) delivery systems to examine whether one project delivery system (PDS) is always superior to the other when it presents lower cost growth. Previous studies have not yet separated the effects of PDS and third factors on cost performance and have thus been unable to determine the most significant factor affecting cost performance in the comparison of DB and DBB. Bidding characteristics tend to increase project costs during the construction phase and have been recognized as the third factors associated with the PDS and cost performance. The current study employed a causal relationship model, using path analysis to distinguish the effect of the PDS and bidding characteristics on cost performance, to identify the third factors as mediators and to determine whether the mediation effect of bidding characteristics has a statistically significant effect on cost growth. Subsequently, it applied a t-test to compare the cost performance of DB and DBB delivery systems across project types, based on 197 public projects in Seoul, South Korea. The results show that the cost performance of DBB has a mediation effect on architectural building projects but not civil infrastructure projects. It indicates a condition wherein DB should not be considered superior to DBB despite the lower cost growth. Thus, PDS have the potential to be misjudged when their cost-effectiveness is mediated by bidding characteristics. This study contributes to the construction engineering and (management body of knowledge by providing a causal relationship analysis to compare DB and DBB cost performance based on a mediation effect. The findings from the study may guide practitioners in the architecture, engineering, and construction (AEC) industry to evaluate and select the appropriate PDS for specific project types and provide a method to benchmark DB against DBB. (C) 2020 American Society of Civil Engineers.