The criticality part of FMECA consists of assigning a number from 1-10 each for Probability and Consequence and a third factor relating to Confidence. Multiplying these 3 gives a criticality number of 1-1000. Thus each failure mode gets a rank based on these 3 numbers. Subjectivity is reduced by using a team approach.
Confidence is largely based on our ability to 'catch' each failure mode in time. Thus a hidden failure will have a high number, while an easily detectable failure gets a low number.
The ranking number, or RPN weights each risk rank (Prob.number x consequence number) by the confidence number.
All the other steps that precede the RPN analysis is common to both FMEA and FMECA.