Systematic vs random
eng(ret'd)
A systematic failure is one caused by an element in the design process and, being systemeatic will occur the same way, caused by the same conditions every time (predictable and repeatable). Therefore, there is no 'median'. Random (wearout) failures are those that will vary with time and for which a median can be established for lifing.
Reminds me of the software guarantee which stated 18 months from date of delivery. Not worth the paper it was written on.
sw