W5_Khalid Almamari_Schedule Estimation Analysis

1. Problem Definition

As previous experience while working on a FEED Project, the project was undertaken by a fenced task where I was assigned as the project engineer. The project duration was given as 11 months by the Client. Unfortunately the Project has been over-run its schedule by additional 2 months. This analysis will study if there was a better way to estimate the schedule duration.

According to the PMBOK the following are the different tools and techniques used to Estimate activity durations:

  1. Expert judgment:
  2. Analogues estimating
  3. Parametric estimating
  4. Three point estimating (PERT)
  5. Group decision making
  6. Reserve analysis

While these methods are all viable, their precision and accuracies differ. If we take a closer look at the three point estimating method we could tell that the precision of these types estimates are much higher and therefore more practical to be used at this stage of the Project.

2. Feasible Alternatives

In this analysis we will be looking at a comparison between two alternative methods:

  • Continue using a combination of Expert judgment and Analogues estimating or
  • Use the more accurate duration estimate using the Three point estimating (PERT)

3. Develop the outcomes for each alternative

  • A combination of Expert judgment and Analogues estimating – based on the time it took to do similar tasks on other projects and based on the experience of Client in similar projects
  • Three point estimating (PERT) – duration based on preferable % probability (usually 80 – 90% probability)

4. Acceptable Criteria

The acceptable criteria for this analysis will be a duration estimate accuracy >90% based on historical data (actual duration).

5. Analysis and comparison of the alternatives

To perform PERT analysis, I have approached some of my experienced colleagues to obtain their input on the time required to complete a similar kind of project with a fenced task. A PERT analysis carried out gave us the following results:

  Time (months)
Min 10
Average 12
Max 14
Mean 12
sigma 0.667
Variance 0.444
P(90) (z=1.29) 13
P(80) (z=0.85) 12

Comparison between alternatives:

Method Duration Estimate
Client Estimate 11 months
PERT (P90)  13 months
PERT (P80) 12 months

The result shows that using the PERT (P90 or P80) will give us a better estimate that fits within our acceptable criteria of > 90% accuracy.

6. Select the preferred alternative

Based on analysis result, PERT P90 shows that the duration estimate is exactly the same with actual duration. The P80 analysis also gives us an accuracy of greater than 90% which would also be acceptable. The client estimate can be seen as less accurate and more of a time driven schedule.

7. Performance Monitoring & Post Evaluation of Result

It is advised that the schedule should be analyzed between a time to a time the project progressing further and more information available to get more accurate results. It is also advised that the schedule is analyzed in a more detailed manner for example looking into the duration of each task and analyzing each task on its own.


  1. Martin, D. (2014, March 25). Estimation Part 2 – Accuracy vs Precision. . Retrieved June 12, 2014, from http://www.dontpanicitsolutions.com.au/lean-thinking/53-estimation-part-2-accuracy-vs-precision/53-estimation-part-2-accuracy-vs-precision
  2. Estimating Time Accurately: Calculating Realistic Project Timelines. (n.d.). Estimating Time Accurately. Retrieved August 15th, 2014, from http://www.mindtools.com/pages/article/newPPM_01.htm
  3. Six Methods for the Estimation of Activity Duration in Project Management. (n.d.). Small Business. Retrieved August 15th, 2014, from http://smallbusiness.chron.com/six-methods-estimation-activity-duration-project-management-41782.html

One thought on “W5_Khalid Almamari_Schedule Estimation Analysis

  1. AWESOME posting, Khalid!!! Really nice job on your analysis……….

    Be sure to take the time to read over and understand the GAO’s “Best Practices in Scheduling” http://www.gao.gov/products/GAO-12-120G as I do believe that to be the best single book on practical applied scheduling I have ever seen.

    Be sure to check out Appendix 1 and Appendix 3 as both of those provide an OUTSTANDING checklist you can and should be using to validate not only your own in house schedules, but those of your contractors as well.

    Keep up the excellent work and looking forward to seeing more blogs of this quality coming from you in the coming weeks…

    Dr. PDG, Jakarta

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s