In Figure 4.2 we show the extent of time over/under-runs in Stage 3: i.e. after the signing of Contract Commitments up to the Actual Final result. A positive association between the size of the project and time over-run (which is statistically significant with 99.9 percent confidence) is evidenced in the case of Traditional projects, but no such association is apparent in PPP projects.
As with the optimism cost bias discussed above, we find that the dispersion of completion timing bias outcomes is also greater in the Traditional projects compared with PPPs.
Traditional projects have been found to be more uncertain than PPP projects for delivery on-time, and Traditional procurement becomes more unfavourable the larger the size of the project.