Ruben Ndihokubwayo

A rework probability model: a quantitative assessment of rework occurrence in construction projects

Statistical methods for eliciting probability distributions were used to analyse the data collected from 78 construction professionals. The empirical distributions for rework costs were found to be non-Gaussian. Theoretical probability distributions were fitted to the rework data. Non-parametric tests were used to determine the goodness-of-fit of the selected probability distributions. The results of the goodness-of-fit tests revealed that generalized Pareto distribution provided the best fit for the dataset. Single probability points for rework from 1% to 10% were calculated. It was established that rework can make a significant contribution to a projects cost overrun. The mean total rework cost as a percentage of the original contract value was found to be 5.12%. For a mean total rework cost of 5.12% the likelihood that a project exceeds is 76%. The anticipation that rework will occur, using the probabilities that are derived, can enable a quantitative risk assessment to be undertaken, which will ultimately lead to identifying alternative solutions so as to avoid rework prior to the commencement of construction work.