**Three-Point Estimation** #

**Three-Point Estimation** is a technique used in project management and Agile methodologies to estimate the duration or effort required to complete a task or user story. It involves estimating three values:

**1. Optimistic Estimate (O)**: The best-case scenario where everything goes better than expected.

**2. Pessimistic Estimate (P)**: The worst-case scenario where everything goes wrong.

**3. Most Likely Estimate (M)**: The most probable scenario based on normal conditions.

The final estimate is calculated using these three values to provide a more realistic and comprehensive view of the task’s effort or duration.

**Formula** #

The final estimate (E) is calculated using the formula:

E=O+4M+P6E = \frac{O + 4M + P}{6}E=6O+4M+P

This formula is known as the **Program Evaluation and Review Technique (PERT)** estimate, which provides a weighted average, giving more weight to the most likely estimate.

**Steps of Three-Point Estimation:** #

**1. Identify the Task**:

**–** Select the task or user story to be estimated.

**2. Estimate the Three Values**:

**– Optimistic Estimate (O)**: Estimate the minimum effort/duration if everything goes perfectly.

**–** **Pessimistic Estimate (P)**: Estimate the maximum effort/duration if everything goes wrong.

**–** **Most Likely Estimate (M)**: Estimate the effort/duration under normal conditions.

**3. Calculate the Final Estimate**:

**– **Use the formula to calculate the final estimate.

**4. Record the Estimate**:

** – **Document the final estimate and the individual estimates (O, P, M).

**Example of Three-Point Estimation for an E-Commerce Website** #

**Scenario**: The team is estimating the effort required to implement a “Checkout Process” feature for an e-commerce website.

**Participants**:

**– Product Owner**: Eva

**– Development Team**: Alice (Frontend Developer), Bob (Backend Developer), Carol (QA Engineer)

**– Scrum Master**: Dave

**User Story:**

**ID**: PBI-005

**Description**: As a user, I want to complete my purchase through a secure and user-friendly checkout process.

**Acceptance Criteria**:

**– **Users can review their cart items before checkout.

**– **Users can enter shipping information.

**– **Users can choose a payment method and complete the payment securely.

**– **Users receive a confirmation email after successful checkout.

**Three-Point Estimation Session:** #

**1. Identify the Task**:

**– **The team selects the “Checkout Process” feature for estimation.

**2. Estimate the Three Values**:

**Optimistic Estimate (O)**:

**– Alice**: “If everything goes smoothly, we can finish the frontend in 3 days.”

**– Bob**: “The backend integration with the payment gateway might take 2 days.”

**– Carol**: “QA testing could be completed in 1 day if there are no major issues.”

**– O = 3 + 2 + 1 = 6 days**

**Pessimistic Estimate (P)**:

**– Alice**: “If we encounter UI issues, the frontend might take up to 6 days.”

**– Bob**: “Payment gateway integration issues could take 5 days.”

**– Carol**: “QA testing might take 4 days if we find significant bugs.”

**–** **P = 6 + 5 + 4 = 15 days**

**Most Likely Estimate (M)**:

**– Alice**: “Under normal conditions, the frontend should take 4 days.”

**– Bob**: “Backend integration is likely to take 3 days.”

**– Carol**: “QA testing should take 2 days.”

**– M = 4 + 3 + 2 = 9 days**

**3. Calculate the Final Estimate**:

**– **Using the PERT formula:

**– **E=O+4M+P6E = \frac{O + 4M + P}{6}E=6O+4M+P

**– **E=6+4(9)+156E = \frac{6 + 4(9) + 15}{6}E=66+4(9)+15

**– **E=6+36+156E = \frac{6 + 36 + 15}{6}E=66+36+15

**– **E=576E = \frac{57}{6}E=657

** –** E=9.5 daysE = 9.5 \, \text{days}E=9.5days

**4. Record the Estimate**:

**– **The final estimate for the “Checkout Process” feature is 9.5 days.

**Summary of Three-Point Estimation:** #

User Story ID | Description | Optimistic (O) | Most Likely (M) | Pessimistic (P) | Final Estimate (E) |

PBI-005 | Checkout Process | 6 days | 9 days | 15 days | 9.5 days |

**Benefits of Three-Point Estimation:** #

**– Comprehensive View**: Accounts for variability and uncertainty in task estimation.

**– Improved Accuracy**: Provides a more realistic estimate by considering best, worst, and most likely scenarios.

**– Risk Management**: Helps in identifying potential risks and their impact on the project timeline.

**– Team Collaboration**: Encourages team members to discuss and consider different aspects of the task.

**Conclusion** #

Three-Point Estimation is a valuable technique in Agile for estimating the effort or duration required to complete tasks. By considering optimistic, pessimistic, and most likely scenarios, this method provides a more accurate and realistic estimate, helping teams manage uncertainty and plan effectively. The example of estimating the “Checkout Process” feature for an e-commerce website demonstrates how Three-Point Estimation facilitates informed decision-making and consensus-building within the team.