Defect Rate in Scrum

Defects in Scrum – What Are They?

Defects, in the Agile and Scrum context, refer to anything in a product that a stakeholder perceives as ‘wrong.’ These can be bugs, failures, flaws, or errors in an application or program that result in unexpected, incorrect, or unintended outcomes. In a nutshell, they are the gremlins that can derail a project and frustrate your team and customers.

Defect Rate in Scrum – Measuring Quality

One way to gauge the quality of your Agile process is by using the Defect Detection Percentage (DDP). It’s the ratio of defects identified during testing divided by the total defects identified in that testing phase. DDP can give you insights into the quality of your testing process and can be a valuable metric for continuous improvement.

Defect Rate in Scrum – Defect Leakage

Defect Leakage is another crucial metric. It’s the ratio of defects attributed to a stage but only captured in subsequent stages, compared to the sum of total defects captured in that stage and the defects attributed to it but only captured later. This metric reflects the quality of your testing and can help identify areas where defects slip through the cracks.

Measuring Defects in Scrum- A Formula

In Agile and Scrum, measuring defects typically involves various metrics to assess the quality of the software. Here are some common metrics and their definitions:

Defect Density

• Formula: Number of defects / Size of the software
• Definition: It measures the number of defects per unit of code or functionality. A lower defect density indicates higher software quality.

Defect Removal Efficiency

• Formula: (Number of defects found before release) / (Total number of defects)
• Definition: This metric quantifies how effective your testing and quality control processes are at identifying and fixing defects before the product’s release. Higher values indicate better defect removal efficiency.

Defect Leakage

• Formula: (Number of defects found externally after release) / (Total number of defects)
• Definition: It measures the defects that escape into the production environment and are discovered by users after the product is released. Lower defect leakage is desirable.

Defect Acceptance Rate

• Formula: (Number of accepted defects) / (Total number of defects)
• Definition: This metric indicates the percentage of defects that were accepted as part of the product’s release. Ideally, you want to keep this rate low.

Now, let’s address the burning question…

How do we handle defects in Scrum?

It’s essential to have a clear strategy for this. Here are 8 approaches to consider, along with their pros and cons:

1. Fix Defects During the Sprint: Tackle defects immediately, ensuring they don’t pile up. Pros: Faster resolution. Cons: May disrupt the sprint.
2. Add Defects to Product Backlog: Prioritize defects alongside user stories. Pros: Controlled resolution. Cons: May impact planned work.
3. Play Planning Poker: Estimate defect resolution effort. Pros: Better planning. Cons: May be inaccurate.
4. Identify Patterns in Defects: Spot commonalities to address underlying issues. Pros: Prevents recurrence. Cons: Time-consuming.
5. Refine the Definition of Done: Define stricter acceptance criteria. Pros: Fewer defects. Cons: May slow down development.
6. Hold Sprint Retrospectives: Continuously improve by addressing defects. Pros: Ongoing refinement. Cons: Requires time and effort.
7. Elect a Good Product Owner: Effective communication with stakeholders reduces defects. Pros: Proactive prevention. Cons: Depends on team dynamics.
8. Run a Hardening Sprint: A dedicated sprint for defect resolution. Pros: Efficient defect handling. Cons: May disrupt regular work.

What’s a Good Defect Percentage?

A good defect percentage depends on your industry and the severity of defects.

For minor defects, the industry average AQL (Acceptable Quality Level) is around 4%.

Major defects, which are unacceptable to customers, have an AQL of about 2.5%.

Remember, these are just industry averages, and the right threshold might vary for your specific project.

Estimating Defects in Agile

The question of estimating defects in Agile is a topic of debate. Some argue that you can plan without defect estimates by using previous sprints as a baseline. If in the last sprint, you completed 30 story points and fixed 2 bugs, that’s your baseline.

If you have another 30 points of stories in the upcoming sprint, you likely have the capacity to fix a couple of bugs. It’s a pragmatic approach that focuses on past performance rather than speculative estimates.