W5.2_SSG_Re-estimate project duration using PERT method


PROBLEM DEFINITION

Currently we are in the start beginning of Execution phase of Topside EPCI project. The baseline duration has been setup. Prior to Kick of Meeting, management is asking project team to estimate the duration of the project in worst case, normal situation, best case and find the duration that “technically justified”.

DEVELOPMENT OF FEASIBLE ALTERNATIVES

There are some methods applicable to perform risk assessment. One of the methods is PERT (Project Evaluation and Review Technique). This method basically using weighted average of three numbers as follow:

  • The most optimist case (O) where everything is goes right
  • The most pessimist case (P) where everything is goes wrong
  • Most likely case (M) where normal problem and opportunities is applied.

Basic formula of this method is summarized in the formula 1. as follow:

Z = (O + 4M + P)/6

Where:

  • Z = applicable value of Estimate
  • O = optimist case
  • M = Most likely
  • P = Pessimist case

Figure 1. PERT (solid line) vs. Triangle (dotted line)

DEVELOPMENT OF OUTCOMES FOR EACH ALTERNATIVE

Using PERT method, every activity is measured and the value of three numbers (optimist, most likely, and pessimist) are identified and quantified.  The applicable value (Z) is achieved by using formula 1.

Figure 2. Base case duration (month) and Z value duration (month) of each activities.

As seen in the figure.2, the total duration by applying PERT method is increasing from 36.43 month (base case) to 41.43 months.

SELECTION OF CRITERIA

By using the PERT method, it is possible to find the duration of each activity that highly potentially happen during the execution phase by considering of optimist, most likely, and pessimist case. It’s foreseen that each activity has different duration even with most likely ones.

Since the three value (optimist, pessimist, and most likely) is based on the expert judgment (SME), the weighted average of those judgment value is technically accepted.

ANALYSIS FOR THE ALTERNATIVES

Figure.3. Bar Chart of Duration (Base case) and PERT applied

Figure.4. S Curve and Monthly unit duration (Base case) and PERT applied

Based on above Bar Chart on figure.3, it is seen that all the phase has tendency to be delay compared to base case. It means that our base scenario and the duration is subject to “too optimist”.

In the figure 4. It is seen also unit duration of Base case and PERT applied is vary every month depend on the activities held on that month.

SELECTION ON THE PREFERRED ALTERNATIVES

As per request of the management is to identify the duration of the project in the case of optimist, most likely, pessimist, and “technically justified”, the PERT method is applicable.

In summary, the total duration that “technically” justified for the project is 41.43 months.

 

PERFORMANCE MONITORING AND POST EVALUATION RESULT

The result of PERT assessment is need to be updated periodically i.e. quarterly. This is important in order all assumption that is made in beginning of the project still valid

REFERENCES

Giammalvo, P.D.  (2013). AACE Certification Preparation  Course-2nd day module. (pp 63-66). Jakarta.

Mochal, T.  (2007). Use PERT technique for more accurate estimates. Retrieved on November 29,2013 from  http://www.techrepublic.com/blog/it-consultant/use-pert-technique-for-more-accurate-estimates/

PM Knowledge Center (2013). The Program Evaluation and Review Technique (PERT): Incorporating activity time variability in a project schedule. Retrieved on November 29,2013 from  http://www.pmknowledgecenter.com/node/59

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1 Comment

Filed under Hadianto P, Week 05

One response to “W5.2_SSG_Re-estimate project duration using PERT method

  1. MUCH better this time, Pak Sutoyo!!!

    BR,
    Dr. PDG, Geneva, Switzerland

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