An Examination of Randomized Inspection Schedules with Respect to Two Detection Criteria

Three broad classes of schemes for randomizing inspection schedules are examined in light of two inspection criteria: average or expected time to detection, and probability of timely detection. It is shown that among two classes of inspection schemes, for the criterion of average detection time, no scheme performs better than a simple periodic inspection schedule. A simple periodic inspection schedule is also optimal for the probability of timely detection criterion when adequate inspection resources are available; if this is not the case, the optimal strategy is shown to be one in which inspection opportunities at fixed intervals are "sampled" or chosen randomly with a fixed probability.