Statistical concepts and data requirements for valid failure rate estimation

The distinction between point estimation and confidence interval estimation for failure rates is described. Why the upper bounds of failure rate confidence intervals are prescribed by safety standards for use in safety metric computations is explained. Statistical formulas for the failure rate upper bounds are provided. The requirements that the field failure data (FFD) must meet to ensure the validity of the failure rate estimations are discussed from both mathematical and engineering perspectives. The need to understand the underlying causes of failure in determining when FFD can be aggregated is explained. Examples illustrating the impacts on failure rate estimation when the data requirements are and are not met are presented.