Let’s consider the simplest example, which is two equally probable events connected by an OR gate (or in parallel). Assume a constant probability of 0.1 for both events A and B. Because the events have equal probability, it is expected that each event would have the same importance measure.

Using the formulae presented earlier in this document for importance measures, the Birnbaum importance measure for both events A and B is 0.9. Similarly, the Criticality and Fussell-Vesely importance measures are the same for both of these identical events. Therefore, for this system, the importance measures are the same for both events.

If these two equally probable events are connected by an AND gate, the identical events are still equally important. For example, the Birnbaum importance measure would be 0.1 for both events A and B.