Yes, Neil; as you know, I'm a supporter of the "Risk-Based PM Model" ... but again, to start with the risk assessment is simply predictive
(based upon an informed Best Guess), and in any case usually only sets the initial interval between PM visits. Only after a few - or perhaps, many - PM cycles does a true pattern of equipment reliability emerge.
At that stage, a good PM system allows adjustments to be made - generally reducing or increasing the interval between PM visits accordingly, as well as (possibly) reviewing the Risk Factor(s) settings.
In many situations I have seen (or should I say, suffered
) - and, indeed, studied - the PM schedule never reaches that happy state of equilibrium (that is, too few PM cycles on which to base an informed judgement).
With PM (and as you know), you have to be in it for the Long Haul.