Weighted Shortest Job First (WSJF)

Weighted Shortest Job First (WSJF): A Comprehensive Guide

Why WSJF is Important

Weighted Shortest Job First (WSJF) is a prioritization model that plays a crucial role in business analysis and project management, especially in agile environments. It's important because:

• It provides an objective, quantitative approach to prioritization
• It helps teams maximize the economic benefit of development efforts
• It aligns with lean and agile principles by focusing on delivering high-value items first
• It considers both business value and time sensitivity
• It supports data-driven decision making, reducing subjective biases

What is WSJF?

WSJF is a prioritization technique developed as part of the Scaled Agile Framework (SAFe). It's a calculation model used to sequence jobs (features, capabilities, or epics) to produce maximum economic benefit. The model is based on the principle of minimizing cost of delay by doing the shortest, highest-value jobs first.

At its core, WSJF is a ratio of two factors:

WSJF = Cost of Delay ÷ Job Size

Where:
• Cost of Delay (CoD) represents the economic impact of delaying the job
• Job Size represents the effort required to complete the job

How WSJF Works

Step 1: Calculate Cost of Delay

In the SAFe framework, Cost of Delay is determined by combining three factors:

Cost of Delay = User-Business Value + Time Criticality + Risk Reduction-Opportunity Enablement

Where:
• User-Business Value: The relative value to customers and business
• Time Criticality: How time-sensitive the job is (includes fixed deadlines, first-mover advantage, etc.)
• Risk Reduction-Opportunity Enablement: The value of reducing risks or enabling future opportunities

Each of these three factors is typically rated on a scale (often using the Fibonacci sequence: 1, 2, 3, 5, 8, 13, 21) with higher numbers indicating higher value.

Step 2: Estimate Job Size

Job Size is estimated using relative sizing, often using story points or t-shirt sizes converted to numeric values. This represents the effort, complexity, or resources required to complete the job.

Step 3: Calculate WSJF

Divide the Cost of Delay by the Job Size:

WSJF = Cost of Delay ÷ Job Size

Step 4: Prioritize based on WSJF score

Items with higher WSJF scores are prioritized higher. This means you're delivering the most value per unit of effort first.

Example:

Feature A: CoD = 20 (BV:8, TC:5, R/OE:7), Job Size = 5, WSJF = 4
Feature B: CoD = 10 (BV:3, TC:3, R/OE:4), Job Size = 2, WSJF = 5
Feature C: CoD = 15 (BV:5, TC:8, R/OE:2), Job Size = 8, WSJF = 1.875

Based on WSJF, the priority order would be: B, A, C

Exam Tips: Answering Questions on WSJF

1. Know the formula
Memorize the basic formula: WSJF = Cost of Delay ÷ Job Size
And remember that Cost of Delay = User-Business Value + Time Criticality + Risk Reduction-Opportunity Enablement

2. Understand the scales
• Know that relative scaling is typically used (often Fibonacci numbers)
• Higher numbers mean higher value/bigger size
• The purpose is to compare items relatively, not to assign absolute values

3. Watch for calculation questions
• Practice calculating WSJF given the component values
• Be careful with the arithmetic - remember it's CoD divided by Job Size
• Check that higher WSJF scores indicate higher priority

4. Look for conceptual understanding questions
• Understand that WSJF aims to maximize economic benefit
• Know that it favors high-value, low-effort items
• Recognize it as a technique suitable for agile and lean approaches

5. Be ready for application scenarios
• Practice applying WSJF to scenario-based questions
• Pay attention to clues about business value, time sensitivity, and effort
• Remember that the goal is to get the most value delivered quickly

6. Common pitfalls to avoid
• Mixing up the numerator and denominator
• Forgetting that all three components contribute to Cost of Delay
• Assuming higher raw CoD always means higher priority (job size matters too)
• Thinking that WSJF is only about business value (time criticality and risk/opportunity are equally important)

7. Context considerations
• Recognize when WSJF is appropriate (and when it might not be)
• Understand its relationship to other prioritization techniques
• Know that it's particularly useful in scaled agile environments

When studying for your PMI-PBA exam, make sure you can both calculate WSJF correctly and understand the underlying principles that make it valuable as a prioritization technique.