Cost Performance Comparison of Design-Build and Design-Bid-Build Focusing on Mediator Effect

Abstract

According to previous research, the reason why Design-Build(hereinafter referred to as DB) outperforms Design-Bid-Build(hereinafter referred to as DBB) in terms of cost is due to less change orders. However, if biddropping was low for DBB resulting into change orders, and little difference between completion cost and budget cost, then it would be wrong to conclude that DB is superior due to less change orders. Therefore, in order to confirm such misjudgment, the attempt to comprehensively analyze biddropping, change order and delivery method were made as previous methods had analyzed either the relationship between delivery method and change order, or biddropping and change order. This research uses a path analysis, which simultaneously compares effect sizes on change orders according to delivery method and biddropping based on the project type, and validated the mediator effect. The research proved that validating DB is superior to DBB due to less change orders cannot be validated as biddropping caused a mediator effect by intervening between the delivery method and change order for specific project types. Therefore, the mechanism of delivery method acts on change orders through biddropping was established. Also, the identity of biddropping was investigated in a different approach from previous research. Based on this result, this research is expected to help determine a delivery method by considering the mediator effect of specific projects and evaluate performance of the selected delivery method.