Make sure you agree on the meaning of the jargon.
If you had to vote would you say that the expressions “more selective” and “higher selectivity” are different ways of expressing the same idea, or are they exact opposites of each other ? I think I can safely say that I have seen people waste a ludicrous amount of time arguing past each other and confusing each other because they didn’t clarify their terms (and one, or both, parties actually misunderstood the terms anyway).
Selectivity is a value between 0 and 1 that represents the fraction of data that will be selected – the higher the selectivity the more data you select.
If a test is “more selective” then it is a harsher, more stringent, test and returns less data (e.g. Oxford University is more selective than Rutland College of Further Education): more selective means lower selectivity.
If there’s any doubt when you’re in the middle of a discussion – drop the jargon and explain the intention.
If I ask: “When you say ‘more selective’ do you mean ….”
The one answer which is absolutely, definitely, unquestionably the wrong reply is: “No, I mean it’s more selective.”