> filter down from a large number ... to a small number ... doesn't say anything about how selective they are.
But that's what the definition of "selectivity" is for database retrieval. Selectivity == n_rows_selected/n_row_count. The "larger number" was the denominator and the "small number" was the numerator.
Your example SQL is not consistent with your previous sentence:
SELECT TOP 1000 FROM resumes ORDER BY received_date
Notice that nowhere is the total row count for resumes known in your isolated example? So yeah, we don't have the denominator to determine selectivity.
For examples of Harvard and Google, we know the denominators (the total applications and total resumes). Therefore we know the selectivity.
I suspect you're mixing up "mathematical selectivity" from "decision process selectivity" because Google's internal decision tree for hiring might look to outsiders as "black box" or nonsensical.
The denominator has no relevance to how selective your hiring process is. Your process does not become more exacting and precise simply because you received more applicants.
Thank you for confirming that you were using the colloquial version of "selectivity" which doesn't require knowing the denominator instead of mathematical "selectivity" which does.
That wiki page orders the ranking on mathematical selectivity and not colloquial selectivity. My previous comment of Google Inc being more "selective" than Harvard is to be interpreted as mathematical selectivity. Sorry for not stating it more explicitly to prevent confusion.
So you don't care about on what basis selection is performed?
If your assertion is just that Google rejects a higher proportion of applicants than Harvard, that's... not at all interesting. The lottery rejects and even larger proportion of applicants for its 'grant' program, but I'm not going to try to learn anything from how it goes about picking winners.
But that's what the definition of "selectivity" is for database retrieval. Selectivity == n_rows_selected/n_row_count. The "larger number" was the denominator and the "small number" was the numerator.
Your example SQL is not consistent with your previous sentence:
Notice that nowhere is the total row count for resumes known in your isolated example? So yeah, we don't have the denominator to determine selectivity.For examples of Harvard and Google, we know the denominators (the total applications and total resumes). Therefore we know the selectivity.
I suspect you're mixing up "mathematical selectivity" from "decision process selectivity" because Google's internal decision tree for hiring might look to outsiders as "black box" or nonsensical.