The Cost of Software Bugs

The cost of fixing software bugs increases exponentially as the development life cycle progresses.

Studies by Dr. Barry W. Boehm at GTE, TRW, and IBM in the late 1980s came to the following conclusion: errors are typically 100 times more expensive to correct in the maintenance phase on large projects than in the requirements phase.

The old saying "an ounce of prevention is worth a pound of cure" applies here.  Implementing a balanced QA strategy that gives equal attention to preventing bugs as well as finding them is a sound business decision.

In QA jargon, the Return On Investment (ROI) for preventing vs. fixing bugs is called Cost of Quality (COG).  There are 3 COQ categories:

  1. Prevention
  2. Appraisal
  3. Failure

Prevention is an effort to avoid the creation of errors.  The investment comes in the form of establishing QA methods & procedures, plus the training of staff in the use of QA practices.  Spending money here will help to prevent errors from occurring in the first place via the implementation and consistent execution of QA procedures.  Think of this as "value investing" (i.e. make the upfront investment in solid practices now for long-term,positive growth).  This category has the highest ROI.

Appraisal occurs during development.  Costs come in the form of product reviews, code inspections, and testing.  This category has a lower ROI because finding and fixing discrepancies is more expensive (due to re-work), than preventing them.

Failure has the lowest ROI.  Previously undetected defects are found and must be fixed.  In the pre-delivery phase it involves costly redesign, recoding, and testing.  Post delivery, it can trigger refunds and loss of customers.

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