This International Standard provides statistical methods for evaluating point estimates, confidence intervals, prediction intervals and tolerance intervals for the failure rate of items, whose time to failure follows an exponential distribution. This implies that the failure rate (see IEV 191-12-02) is constant with respect to time. It should be noted that although reference is made above to failure rate, the numerical methods to be described are equally applicable to other event rates provided the times to the occurrence of the event follow an exponential distribution. Thus, with this qualification, the numerical methods will apply, for example, to constant failure intensities and constant repair rates (see IEV 191-12-04 and IEV 191-13-02 respectively). For convenience, however, and to avoid unnecessary repetition, reference will be made in what follows only to failures and failure rates.

Use of the procedures in this standard should be supported by tests to confirm the validity of the assumption of constant failure rate or failure intensity (see IEC 60605-6).

This standard is also applicable whenever a random sample of items is subjected to a test of times to failure for the purpose of estimating measures of reliability performance.