In discussions of probability we often find ourselves saying that we can make an event more likely or less likely. It feels wordy, like there should be a single word for that. I don't mean "preclude" or "necessitate." I mean a change of probability that doesn't reach 0% or 100%. For example, we might say:
If we increase the sample size, we [decrease the probability of] certain kinds of error. If we decrease the sample size, we [increase the probability of] certain kinds of error.
What goes in that bracketed space? Not "rarify," which means something else; and not "preclude," which we can never seem to accomplish.