What are paybacks from inspections

The key reason for inspections is to obtain a significant improvement in software quality, as measured by defects that are found in the product when it is used. A project example from AT&T the Integrated Corporate Information System shows the inspections for a portion of ICIS.
Project:
Data base accounting
14 persons
3 month duration
20 modules; 7,000 LOC
Inspection Results:
Analysis 23 defects High-level design 83 Detail design 85 Code 77 ----------------------------------- Totals: 268 defects 37 inspectionsEvaluation:
Product delivered on-time, within budget
Only 4 defects found in product
Stability Index* of 0.2% vs. 15% expected
Development personnel very favorable where Stability Index = % LOC Maintained/Total LOCThe evaluation indicates the high quality of the resulting product. Nevertheless, as Mike Fagan pointed out in 1976 that inspections shorten the development schedule, the productivity will increase as the inspections perform formally. In addition, it should be expected that the development timescale, testing cost, and lifetime cost will be reduced and manageability of the development process will be improved.