📘 PERT (Program Evaluation and Review Technique)
🔹 1. Definition
PERT (Program Evaluation and Review Technique) is a project scheduling technique used to estimate the time required to complete a project when activity durations are uncertain.
👉 It focuses on probabilistic time estimation (uncertain environments).
📌 Developed for R&D and complex projects.
🔹 2. Key Idea of PERT ⭐
PERT assumes that activity time is not fixed but can vary.
So it uses three time estimates:
- 🟢 Optimistic time (O) → Best case
- 🟡 Most Likely time (M) → Normal case
- 🔴 Pessimistic time (P) → Worst case
🔹 3. PERT Formula
🔸 Expected Time (TE)
TE = (O + 4M + P) / 6
👉 This gives a weighted average time estimate.
🔹 4. Standard Deviation and Variance (Important ⭐)
🔸 Standard Deviation
SD = (P − O) / 6
🔸 Variance
Variance = [(P − O) / 6]²
🔹 5. Steps in PERT
🔸 Step 1: Identify Activities
- Break project into tasks (WBS)
🔸 Step 2: Define Dependencies
🔸 Step 3: Draw Network Diagram
- Show activities and relationships
🔸 Step 4: Assign Time Estimates
- O, M, P for each activity
🔸 Step 5: Calculate Expected Time
🔸 Step 6: Find Critical Path
- Longest expected time path
🔹 6. Example
Calculation:
TE = (2 + 4×4 + 6) / 6
= (2 + 16 + 6) / 6
= 24 / 6 = 4 days
🔹 7. PERT Diagram Description
📌 PERT uses a network diagram (AON/AOA):
- Nodes → Activities
- Arrows → Dependencies
- Each activity shows O, M, P or TE values
- Critical path is highlighted
🔹 8. Advantages of PERT
- Useful for uncertain and new projects
- Improves time estimation accuracy
- Helps in risk analysis
- Identifies critical activities
- Supports planning of complex projects
🔹 9. Limitations of PERT
- Time-consuming calculations
- Depends on accurate estimation of O, M, P
- Not suitable for simple projects
- Assumes probability distribution (may not always be accurate)
🔹 10. PERT vs CPM ⭐ (Very Important)
| Feature |
PERT |
CPM |
| Time Type |
Probabilistic |
Deterministic |
| Focus |
Time uncertainty |
Cost & time |
| Estimates |
3 (O, M, P) |
Single estimate |
| Use |
Research projects |
Construction/software |
| Nature |
Flexible |
Fixed planning |
🔹 11. Key Terms
- Optimistic time (O) → fastest completion
- Most likely time (M) → normal condition
- Pessimistic time (P) → worst case
- Expected time (TE) → weighted average
🔹 12. Importance of PERT
- Helps manage uncertain project timelines
- Improves planning accuracy
- Useful for large and complex software projects
- Supports decision-making under risk
🔹 13. Short Summary
- PERT is a probabilistic scheduling technique
- Uses three time estimates: O, M, P
- Calculates expected time using weighted formula
- Best suited for uncertain and research-based projects
🔹 14. Quick Exam Answer (2–3 lines)
PERT (Program Evaluation and Review Technique) is a project scheduling technique used to estimate project duration under uncertainty. It uses three time estimates—optimistic, most likely, and pessimistic—to calculate expected time using a weighted average formula.
🔹 15. Likely Exam Questions
- Define PERT.
- What are O, M, and P times in PERT?
- Write PERT formula for expected time.
- Differentiate between PERT and CPM.
- What are the advantages of PERT?
- Explain standard deviation in PERT.
- Draw and explain a PERT network diagram.