Engineers want to know how things work. Reliability engineers want to know how and when things fail. My goal has been to help engineers and service providers learn and use age-specific field reliability; that is, what really happens to products in the hands of customers as a function of age, because the data and methods are available, the needs are great, and we may get fired if we don’t produce credible reliability predictions!

Reliability engineers recognize that MTBF prediction methods don’t represent age-specific field reliability. MTBF is not age-specific. These engineers are paid for accurate, precise, and defendable predictions that give just cause for design, process, and service actions, so I try to help them make the best reliability predictions possible, objectively, accurately, and precisely, using all available data and information.

This monograph describes methods to extend MTBF prediction to complex, redundant, dependent, standby, and life-limited systems. It also describes a credible method for predicting age-specific field reliability, using observed reliability of comparable products or parts. Finally, this monograph adapts insurance credibility to update predictions as user data becomes available.

Chapters 2 and 3 summarize the MTBF prediction state of the art and criticize it. Chapter 4 extends MTBF prediction methods and corrects a common error. Chapter 5 describes the best of all possible worlds, in which people acquire old product user data, incorporate it in reliability predictions, use them, modify them as new product user data accumulates, plan for obsolescence, and feed reliability information back to repeat the process; statistically sufficient data is available to support age-specific reliability predictions for all products and service parts, without life data. Chapter 6 proposes a method for making age-specific reliability predictions by using observed reliability and MTBF predictions for comparison products. Chapter 7 adapts insurance credibility to update reliability predictions as user data accumulates. Chapters 4, 6, and 7 provide extensions to MTBF and reliability prediction and to incorporating field data as it becomes available.  Chapter 8 describes an MTBF prediction workbook and spreadsheet implementations of the MTBF and reliability prediction extensions in chapters 4, 6, and 7.

Preface to Second Edition

I am grateful to the American Society for Quality Reliability and Risk Division and to Chair Dan Burrows for allowing the copyright of "Credible Reliability Prediction" to revert to the author so I could revise, correct, and release this 2nd edition. Click on the title page to open it in new tab and read it. 

I wrote “User Manual for ‘Credible Reliability Prediction’” to provide help and live spreadsheet images, to expand on some of the subjects, and to include developments since  ‘Credible Reliability Prediction.’ Digital version of the User Manual is below the "Credible Reliability Prediction" tab. Click on it to open in new tab and read it.