A qualification procedure may comprise different rests which may either be successful or a failure. However, there are cases of degradation which should be taken into account. The reliability of a consecutive k-out-of-n:G set of tests is evaluated, along with the possibility of degradation. The problem is formulated as a difference equation that is transformed into a digital filter equation. Numerical results indicate improved chances of success for a set of tests that take into account the case of degradation. (C) 2001 Elsevier Science Ltd. All rights reserved.