There exists a great number of studies that have been conducted in the construction industry that concern the causes of lost productivity. However, these studies have two major shortcomings: first, that they do not consider a breadth of factors and second, that they do not provide statistical evidence for the impact the factors they consider may have on labor productivity. This study fills this gap by developing a "quantitative" and "qualitative" analysis of a comprehensive list of productivity factors using extensive data from 167 completed mechanical and electrical construction projects. The quantitative analysis of this paper showed strong statistical evidence that multiple labor factors can have high impact on the overall project productivity. "Longer change order processing time" corresponded to the highest productivity loss (17.75%) in the data, whereas ''overtime use" corresponded to a lower productivity loss of (7.06%). Based on the qualitative analysis, it was found that 'out-of-sequence work' impedes project performance the most, followed by "trade stacking" and "access constraints." These results provide statistical evidence for productivity loss based on the presence or absence of a factor-they are not, however, intended to provide exact values for the amount of productivity lost for any one factor.
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