Defect Trends
This guideline describes how to measure and use defect arrival/close trends.
Main Description

Overview

This is a trend chart showing the rate of defects arrival and closure (fixing) over the project duration. Use this chart to ensure that arrival and closure rates have some correlation (i.e. that your arrivals don’t consistently outpace your closure, resulting in a high defect backlog), to determine the remaining defect backlog, to project the future defect arrival/close rate up to and post-ship.

Measurement Method 

Count

  • Number of defects found and closed each unit of time (usually week, but could be day or month, depending on iteration length). Graph over time, typically in 2 lines.
    • Can also superimpose bars of “remaining defects” over the line graphs, as this may not always be evident. (The close rate can exceed the arrival rate for one or more data points, which can obscure the backlog.)
  • Total cumulative defects found and closed. Graph over time, typically in 2 lines. In this case, the difference between the 2 lines shows the defects remaining (not including any backlog that predates the collection of arrivals.)

Measurement Analysis

As the end of cycle (ship date) nears, should expect to see arrival rate slowing and closure rate surpassing it, indicating that fewer defects are being found (hopefully because you’ve found them already) and any backlog or outstanding defects are being fixed. If the arrival curve does not taper down, it suggests you may continue to find defects post-ship. In the cumulative chart, expect to see the gap narrow between “total found” and “total fixed”. If a large gap remains, you have many defects still not closed that may necessitate lengthening the schedule or shipping with unclosed defects.

Note that looking purely at arrivals and closure does not include defects in a backlog that predates the data collection.

Use this metrics in conjunction with Defect Density at Customer Ship