A Deep Dive into PERT Estimation

PERT: What is it?

PERT is an acronym for Program Evaluation & Review Technique, and was developed by United States Defence as a quick estimating strategy in 1950’s. It is also known as Three-Point technique or PERT Weighted Average. PERT can be used to apply to Costs, and Schedules. 

 

Understanding the PERT Estimation

PERT emphasis on Three-Point estimate for each Project activity incorporating Optimistic(O), Pessimistic (P), and Most Likely (M) time estimates.

The Formula to Calculate Expected Duration (TE) for an activity is 

TE = O+4M+P

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This formula considers a weighted average, giving more weight to the most likely estimate. The resulting Expected Duration provides a more realistic view of the time required for an activity, considering both optimistic and pessimistic scenarios.

 

Key Components of PERT Estimation

Optimistic estimates (O):

The best-case scenario estimate, representing the minimum time required to complete an activity without any risks and favorable situation.

Pessimistic Estimate (P):

The worst-case scenario estimate, indicating the maximum time needed for activity completion Including Risks and an unfavorable situation.

Most Likely Time (M):

The most realistic and probable time estimate based on historical data and expert judgment, including favorable & unfavorable situations.

Let’s look at an example below. 

 

Sl..no..	Activities	Optimistic time(O) In Days	Most likely time (M) In Days	Pessimistic time (P) In Days	Expected Duration TE = (O+4M+P)/6  In Days
1	Requirement Analysis	10	15	20	15
2	Development	20	30	40	30
3	SIT/Functional Testing	12	18	23	18
4	UAT Testing & Support	10	15	22	15
5	Production Deployment	4	6	10	6
6	Hypercare/Warranty Period	10	15	23	16
	Total TE Project				100

Table 1

Note: The above Activities can be broken down into smaller tasks. I have taken an Abstract of Activities for Illustration only.

 

Let’s Assume the Project Start Date as 06-Dec-2023

 

Sl..no..	Activities	TE	Start Date	End Date
1	Requirement Analysis	15	06-Dec-2023	21-Dec-2023
2	Development	30	21-Dec-2023	20-Jan-2024
3	SIT/Functional Testing	18	20-Jan-2024	06-Feb-2024
4	UAT Testing & Support	15	06-Feb-2024	22-Feb-2024
5	Production Deployment	6	22-Feb-2024	28-Feb-2024
6	Hypercare/Warranty Period	16	28-Feb-2024	15-Mar-2024

Table 2

Note: Some of the above dates fall on Weekends, and this is just for Illustration Only

Now, let’s build a Timeline Chart using Table 2.

 

To Create the Timeline Chart in Google Sheets

1. Select the above Table 2 (Data Range i.e Sheet1!C16:G22) in the example (Attached Google Sheet Below for Reference)
2. Click on Insert → Select & Click on Timeline 
   
3. Map the Column from Table 2 on Required fields (Settings) on the left pane to the following
   • Start Date -> Start Date
   • End Date or Duration -> End Date
   • Card Title -> Activities

 

Timeline Chart in Google Sheet

Link to the spreadsheet: PERT Estimation_Example

Benefits of PERT Estimation

1. Probability Analysis: PERT estimation embraces a probabilistic methodology, offering a spectrum of potential durations for each activity. This contributes to the assessment and management of risks within the project.
2. Improved Accuracy: PERT estimation provides a more detailed and precise depiction of project timelines when contrasted with conventional single-point estimates.
3. Effective Resources Allocation: Project managers can better allocate resources by understanding the variability in activity durations. This promotes optimal resource utilization.
4. Risk Mitigation: PERT estimation highlights critical path activities and potential bottlenecks, allowing project teams to focus on risk mitigation strategies.

By embracing the three-point/PERT estimation methodology, Project Managers/Sales/Developers/Testers can navigate uncertainties, enhance decision-making, and steer their teams toward successful project completion. PERT estimation is not merely a mathematical tool; it’s a strategic ally in the pursuit of project success, offering a holistic view that empowers teams to adapt, innovate, and thrive in the face of complexity.