Time performance results are presented as Tables 8 to 10 below.
Table 8 Time over-runs: Traditional and PPP projects relative to the expected time at the start of the period under consideration (based on averages) (source: Duffield 2008)
| Full period | Stage 1 | Stage 2 | Stage 3 | |
| No of observations | 30 | 30 | 24 | 39 |
| 15.4% | -4.0% | 18.1% | 25.9% | |
| PPP projects | 17.4% | 14.8% | 11.7% | 1.4% |
| Difference (Traditional - PPP) | -2.0% | -18.8% | 6.4% | 24.5% |
The average results for time as presented in Table 8 indicate there is very little difference between PPPs and Traditional projects over the full period (the difference is statistically insignificant). There is however major differences between the procurement approaches during the different periods, in particular, PPPs perform very well (1.4% over-run) once a contract is signed. This compares with a relatively poor performance from Traditional projects where there is a time over-run of 25.9% on average.
Percentile results are presented as Table 9.
Table 9 Time over-runs: Traditional and PPP projects relative to the expected time at the start of the period under consideration (based on median results) (source: Duffield 2008)
| Full period | Stage 1 | Stage 2 | Stage 3 | |
| No of observations | 30 | 30 | 24 | 39 |
| Median (P50) |
10.9% |
0.0% |
3.7% |
7.3% |
| PPP projects: Median (P50) |
5.6% |
0.0% |
8.8% |
0.0% |
| Difference in medians (Traditional - PPP) |
5.3% |
0.0% |
-5.1% |
7.3% |
| Inter-quartile range for Traditional projects (i.e. P75 - P25) | 38.0% | 19.4% | 40.4% | 43.4% |
| Inter-quartile range for PPP projects (i.e. P75 - P25) |
37.7% |
31.5% |
23.6% |
12.0% |
| Difference in Inter quartile range (Traditional - PPP) | 0.3% | -12.1% | 16.8% | 31.4% |
The percentile results for time as presented in Table 9 support the average results and indicate there is very little difference between PPPs and Traditional projects over the full period (the difference is statistically insignificant). Again PPPs perform far better than Traditional projects once a contract is signed (difference 31.4%).
Compatible analysis to that of the NAO study [4] results have also been produced for time, refer Table 10. Unlike the UK finding there appears little difference in time performance between PPPs and Traditional projects based in the acceptability criterion of ± 5%.
Table 10 Time over-runs: Traditional and PPP projects relative to the expected time at the start of the period under consideration (based on number of projects >5% over time) (source: Duffield 2008)
| Full period | Stage 1 | Stage 2 | Stage 3 | |
| No of observations | 30 | 30 | 24 | 39 |
| 57.1% | 28.6% | 50.0% | 52.4% | |
| PPP projects | 50.0% | 37.5% | 50.0% | 27.8% |
| Difference (Traditional - PPP) | 7.1% | -8.9% | 0.0% | 24.6% |