Don’t ask “Why did the tester miss that bug?”

“Why did the tester miss that bug?” is a question I have heard in many places but it is the wrong question. W. Edwards Deming’s philosophy shows that if something has gone wrong we need to look at the process and not blame the individual. A tester can be working in a system that the tester can not change and that creates software that contains bugs. If there are bugs we need to look at the system that produced them.

The “Red Beds Experiment” was regularly conducted by Deming. He first ran the “Red Beads Experiment” in Japan in 1950. The book ”Four Days with Dr Deming” gives an example of how the Yawata Steel Company benefited from changing its process as a result of seeing the “Red Beads Experiment”. In the 1980s and early 1990s, Deming ran the ”Red Beads Experiment” in the USA as part of his seminars for executives.

In the “Red Beads Experiment” Deming asked members of the audience at his seminar to act as Willing Workers, a Secretary, and Inspectors in a factory that makes white beads. Unfortunately, there are red beads, as well as white beads, in the raw material that is delivered to the factory. The Willing Workers are to remove the white beads with a paddle and are given detailed instructions on how to do so. The Inspectors count how many red beads have been removed on the paddle and the Secretary records the results. Each scoop of the paddle by a worker represents a day’s work. Unfortunately, because the raw material contains both red and white beads each scoop of the paddle also contains red and white beads. On day four management is disappointed at the number of red beads being collected in the paddles and develops a plan. The plan recommends keeping only the best workers, so the workers with the worst results that day are laid off. The remaining staff are warned that unless results improve the factory will be closed. On day five the results have not improved as red beds are still being scooped up with white beads, so the factory is closed.

In “The New Economics” Deming lists fourteen lessons from the experiment. One of the lessons is that the Willing Workers were victims of the process as they could not, under the manager’s rules, improve their performance.

Software quality and testers can be victims of the process, like the Willing Workers.  We should not ask “Why did the tester miss that bug?”, we should instead ask how to improve the process.

More Information:

• These two books each give a full account of the “Red Beads Experiment”:
  • W. Edwards Deming The New Economics
  • William J. Latzko, W. Edwards Deming, David M. Saunders Four Days With Dr. Deming

• eLearning from the Deming Institute: DemingNext contains a course on the Red Beads Experiment

• Videos:
  •  Lessons from the Red Bead Experiment (30 minutes)
  • The Red Beads Experiment (38 minutes)