Oracle Scratchpad

July 3, 2014

Philosophy 22

Filed under: Philosophy — Jonathan Lewis @ 9:59 am BST Jul 3,2014

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.”



  1. Hi Jonathan,

    So “higher” here means that it is better in selecting specific data with a very finite count from a large pool of data…
    It translates into being synonymous with having “lower selectivity” because it returns less data and expressed as a ratio having values between 0 and 1 and hence “lower” this value is, the “more selective” the respective thing (plan/clause/predicate) is.

    That is what my understanding is.

    Girish Singhal

    Comment by Girish Singhal — August 14, 2014 @ 2:56 pm BST Aug 14,2014 | Reply

    • Girish,

      I hope you were intending to type “more selective” where you actually typed “higher” in the first sentence, otherwise the “It” in the second paragraph seems to suggest that you think “higher selectvity” is synonymous with “lower selectivity”. This is why it can be so important to describe what you mean – even when you’re thinking the right thing it’s easy to use the wrong word.

      Comment by Jonathan Lewis — August 15, 2014 @ 10:20 am BST Aug 15,2014 | Reply

      • Yes that is correct Jonathan, I meant “more selective” when I said higher there.

        Girish Singhal

        Comment by Girish Singhal — August 15, 2014 @ 11:15 am BST Aug 15,2014 | Reply

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