Analysis of Contribution Table
At this time, the break points for inserting risk factors into the critical path task flow have not been decided upon. The team will come together to do this. In Table 9-1, Task 20—GG is a candidate and Task 30—Assembly is a candidate. Assembly seems to be a good choice because it represents a project's milestone. However, Task 22—Test also has some important characteristics. The test facility is heavily loaded, and the test manager has control over any adjustments in the test scheduling. He or she does not like to make adjustments and can create delays for a project if they miss their scheduled test dates. We can assure ourselves of hitting our scheduled test date if we schedule our first risk factor insertion right after Task 21—II, just before the test task.
| CP Task | Risk Type | Base Estimate Days—M | Longest Estimate Days—W | Delta DaysΔ | Likelihood–Y | Contribution | |
|---|---|---|---|---|---|---|---|
| 1 | A | C | 10 | 13 | 3 | 0.25 | 0.75 |
| 2 | B | C | 12 | 13 | 1 | 0.10 | 0.1 |
| 3 | D | C | 8 | 12 | 4 | 0.30 | 1.2 |
| 4 | G | C | 6 | 7 | 1 | 0.10 | 0.1 |
| 5 | J | C | 13 | 16 | 3 | 0.30 | 0.9 |
| 6 | K | SF | 11 | 12 | 1 | 0.20 | 0.2 |
| 7 | M | C | 3 | 4 | 1 | 0.3 | 0.3 |
| 8 | N | C | 14 | 16 | 2 | 0.4 | 0.8 |
| 9 | P | C | 6 | 7 | 1 | 0.1 | 0.1 |
| 10 | R | C | 4 | 4 | 0 | 0 | 0 |
| 11 | S | C | 3 | 5 | 2 | 0.3 | 0.6 |
| 12 | U | C | 7 | 8 | 1 | 0.1 | 0.1 |
| 13 | V | SF | 2 | 3 | 1 | 0.4 | 0.4 |
| 14 | X | C | 20 | 23 | 3 | 0.3 | 0.9 |
| 15 | Z | C | 10 | 14 | 4 | 0.2 | 0.8 |
| 16 | AA | C | 1 | 2 | 1 | 0.3 | 0.3 |
| 17 | BB | C | 0.5 | 1 | 0.5 | 0.4 | 0.2 |
| 18 | DD | C | 11 | 15 | 3 | 0.2 | 0.6 |
| 19 | FF | C | 6 | 7 | 1 | 0.2 | 0.2 |
| 20 | GG | SF | 8 | 12 | 4 | 0.2 | 0.8 |
| 21 | II | C | 6 | 8 | 1 | 0.2 | 0.4 |
| 22 | Test | SF | 4 | 8 | 4 | 0.2 | 0.8 |
| 23 | KK | C | 2 | 3 | 1 | 0.1 | 0.1 |
| 24 | MM | C | 8 | 10 | 2 | 0.2 | 0.4 |
| 25 | OO | C | 6 | 8 | 2 | 0.3 | 0.6 |
| 26 | PP | C | 1 | 2 | 1 | 0.4 | 0.4 |
| 27 | C | 5 | 9 | 4 | 0.2 | 0.8 | |
| 28 | BA | C | 10 | 11 | 1 | 0.3 | 0.3 |
| 29 | BD | C | 8 | 12 | 4 | 0.2 | 0.8 |
| 30 | Assembly | C | 9 | 11 | 2 | 0.2 | 0.4 |
| 31 | BK | C | 8 | 11 | 3 | 0.2 | 0.6 |
| 32 | C1 | C | 6 | 10 | 4 | 0.2 | 0.8 |
| 33 | C3 | C | 14 | 15 | 1 | 0.2 | 0.1 |
| 34 | C7 | C | 21 | 23 | 2 | 0.2 | 0.4 |
| 35 | CJ | C | 10 | 11 | 1 | 0.2 | 0.2 |
| 36 | CK | C | 8 | 11 | 3 | 0.2 | 0.6 |
| 37 | CL | C | 7 | 8 | 1 | 0.2 | 0.2 |
| 38 | CX | C | 6 | 8 | 2 | 0.2 | 0.4 |
| 39 | C2 | SF | 12 | 20 | 8 | 0.2 | 1.6 |
| 40 | D8 | C | 10 | 12 | 2 | 0.2 | 0.4 |
| 41 | D | C | 3 | 4 | 1 | 0.2 | 0.2 |
| 42 | EA | C | 11 | 12 | 1 | 0.2 | 0.2 |
| 43 | EK | C | 6 | 9 | 3 | 0.1 | 0.3 |
| 44 | EL | C | 4 | 6 | 2 | 0.2 | 0.4 |
| 45 | EM | C | 30 | 36 | 6 | 0.2 | 1.2 |
| 46 | EZ | C | 20 | 25 | 5 | 0.3 | 1.5 |
| 47 | GA | C | 11 | 12 | 1 | 0.2 | 0.2 |
| 48 | GG | C | 8 | 9 | 1 | 0.2 | 0.2 |
| 49 | GZ | SF | 6 | 8 | 2 | 0.3 | 0.6 |
| 50 | I-1 | C | 8 | 9 | 1 | 0.2 | 0.2 |
| 51 | I-2 | C | 8 | 12 | 4 | 0.3 | 1.2 |
| 52 | I-K | C | 8 | 9 | 1 | 0.3 | 0.3 |
| 53 | IL | C | 4 | 6 | 2 | 0.2 | 0.4 |
This is the review the project manager and the team conduct at this risk analysis meeting. The risk factor that they will insert is the sum of the contributions from Task 1 through Task 21, which is 9.4 days (round this up to 10 days). Within this sequence, there are three step function risks, Task 6—K, Task 13—V, and Task 20—GG. Their Δs are respectively 1,1, and 4. With a risk factor of 10, two one-day step functions do not worry us at all. A step function of 4 with a 20 percent likelihood is not a problem either. If there had been a step-function risk of 8 with a 30 percent likelihood, we would not consider the Risk Factor of 10 to be big enough. Therefore, we take half of the risk factor (10/2 = 5), subtract 5 from 8 and add 3 days, making this risk factor 13. However, with the biggest step function being 4 and its likelihood 20 percent, the risk factor of 10 is good.
If there is another “must hit on time” task further along in the sequence we will try to make adjustments to have it preceded by a risk factor. If Assembly (Task 30) is such a task, we have a problem. Eight tasks are not enough to justify full confidence in a risk factor. There simply are not enough tasks to justify the averaging out techniques that we use. The Test Task (#22) is the first task in our second sequence, and it is a step-function task with a Δ of 4 and a 20 percent likelihood. The others are creep risks. Two have Δs of 4; others are relatively small. The calculation contribution summation for the eight tasks adds up to 3.7 days. With only eight tasks, we would not settle for only four days of risk factor even if they were all creep tasks. We feel that we must play it safe but we do not want to unnecessarily pad the time scale. Feeling a little uneasy about using too large a risk factor at this point, we settle on a risk factor of seven days that can be inserted before Assembly (Task 30). Although we may have introduced a project delay of a day or two, we can feel sure that we will arrive at Assembly with all predecessors complete.
Tasks 30 through 53 (Assembly through I L) can make up our last critical path sequence for the project. The sum of the contribution is 12.6 days—we round up to 13 days. We have a step-function Δ of eight days with a 20 percent likelihood for Task 38. Obviously, we need to adjust the risk factor upward. It is reasonable to go with a total risk factor of 15 days. The total of all the Δs in this sequence is 59 days. This number is conservative, but it is not nearly as conservative as if we had simply totaled the longest times for each task. We may not actually use more than the 13 days at the original risk factor, but we can be sure that almost all of it is needed.
Risk factor analysis is not precise. In a world with risks, no one can be precise. Risk factor analysis does keep the buffers reasonable and lets each team member know that although there are buffers, they are needed for real uncertainties and do not allow any room for slacking on task efforts.