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.
Best Answer
A possibility is mitigate
This doesn't apply in the general case of reducing probability, but when you're talking specifically about an adverse condition, reducing its probability also tends to reduce its severity, and I think I've seen the word used in contexts like your example.