If N equals the number of defects originating and found in phase X, and S...

The efficiency rate of error detection for a phase measures how effectively that phase detects defects that originated in the same phase before they escape to later phases. N represents defects both originated and found in phase X. S represents defects that originated in phase X but escaped and were found in later phases. Therefore, the total number of defects originating in phase X is N + S. The detection efficiency for phase X is the portion found within the phase, which is N divided by N + S. Option A reverses the relationship and can produce a value greater than one. Option C is not a rate. Option D is not a valid defect containment formula. The correct formula is N / (N + S).

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