L7

Question 1

What does PERT technique stand for?

Answer 1

Performance Evaluation Review Technique

Question 2

What types of questions can we answer with PERT?

Answer 2

• what’s the probability of it being done in X days
• what’s the completion time, guaranteed with a 95% probability?

Question 3

What does PERT assume?

Answer 3

• the critical path is always the critical path
• activities are statistically independent
• variance of activities is the sum of the individual variances
• project duration is normal distribution

Question 4

What is the standard deviation equation?

Answer 4

Square root of variance

Question 5

What’s the standard deviation equation for the path?

Answer 5

Square root (sum of variances of activities on the path)

Question 6

What is the variance of the completion time?

Answer 6

The sum of the variances on the critical path.

Question 7

What is the expected time to completion?

Answer 7

The sum of expected time on the critical path.

Question 8

Why is the standard deviation equation divided by 6?

Answer 8

Because if you take the tails of the normal distribution (pessimistic, optimistic), they will be 6 sds apart.

Question 9

What is more typically used than PERT in practice?

Answer 9

Simulation software:
- Crystal Ball
- @risk

Overkill if time is low priority
Defo use if time is important

Question 10

Limitations of CPA and Gantt charts?

Answer 10

• durations are hard to estimate
• doesn’t handle resource constraints
• may cause excessive multi-tasking
• complex for large projects

Question 11

Why are project duration/cost estimates so often wrong?

Answer 11

1. Duration estimates are often given large safety margins.
2. Parkinson’s Law says that task durations expand to fill the time available.

• early finish is disadvantageous (new work etc)
• extra time used to polish the result

3. Student syndrome: tasks aren’t started early
4. Murphys Law: the unexpected will happen
5. Time/quality is lost switching between tasks

Question 12

What is a way of mitigating against the estimation problems with CPA?

Answer 12

Use critical chain buffer management.

Question 13

What does critical chain buffer management involve? CCBM

Answer 13

• don’t add safety margins
• mitigates against Parkinson’s law/student syndrome
• remove stigma of late finish
• ask for median time

Question 14

What is a critical chain?

Answer 14

The sequence of precedence and resource dependent elements that prevent projects being completed in less time, given available resources.

Question 15

What’s the difference between critical path and critical chain?

Answer 15

Critical chain also focuses on resources.

If resources were unlimited, they would be the same.

We add a buffer to CCBM.

Question 16

What are the 3 buffers in CCBM?

Answer 16

Project buffer: insert at end of proj.

Feeding buffer: insert at end of task paths feeding critical chain.

Resource buffer: insert when non-critical task precedes a critical one and both share a common resource.

Question 17

What’s the suggested buffer size in CCBM?

Answer 17

50%

Any extra days between what you ask the client for eg 23 days and how long it’ll take eg 21 days.

Question 18

Steps in CCBM:

Answer 18

1. Estimate task durations
2. Determine the projects critical chain(s)
3. Include buffers to protect critical chain
4. Project control
5. Resource allocation

Question 19

What is involved in project control in CCBM compared to traditional?

Answer 19

• traditional: due dates, task completion %
• But with CCBM: monitor state of buffers (and rate at which they deplete)

Question 20

How do you approach resource allocation in CCBM?

Answer 20

Schedule tasks with limited resources first.

Question 21

What are some inevitable problems even with CCBM?

Answer 21

• errors
• oversight
• staff over commitments
• bottlenecks
• imbalances in workload
• slack time is wasted