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I really like the new Stack Exchange home page, where certain questions from the Stack Exchange Network are presented, along with a hotness rating that is described as "arbitrary" in its tooltip.

How do these arbitrary hotness points work?

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Probably the same as…. – kennytm Aug 13 '10 at 13:36
@gnat this question is no longer relevant, there's no hotness involved anymore. Think it's better to cancel the bounty, close this one and post new question if you like. :) – Shadow Wizard Oct 1 '13 at 9:28
@ShaWizDowArd how's that? there's a page the question refers to, and there is "Hot Questions" link there. As for the "new" question, I've got one already thank you; with 6 bounties it appears like going just fine – gnat Oct 1 '13 at 9:40
@gnat nope. The question here is talking about the home page of Stack Exchange. Screenshot - it used to show hot questions in there and changed to show recent active questions at some point. – Shadow Wizard Oct 1 '13 at 9:51
@ShaWizDowArd I see, that's interesting. I added comment asking answerer to clarify on that – gnat Oct 1 '13 at 10:27
@gnat also, the full hot questions list is exactly the same as the list in the collider, plus 50 more. No tweaks anymore... but let David confirm that. :) – Shadow Wizard Oct 1 '13 at 10:34
@ShaWizDowArd according to David, the answer is still correct. This alone made this question worth of the bounty to me. :) Will award the bounty asap (UI says "in 20 hours"), then I think it would better be closed as a duplicate of "what formula..." – gnat Oct 1 '13 at 12:52
@gnat cheers, +50 to David. ;) – Shadow Wizard Oct 1 '13 at 12:54
see also: What changed in the Hot Questions sidebar algorithm? – gnat Feb 26 '14 at 11:22
up vote 52 down vote accepted

Basically what's documented here:

What formula should be used to determine "hot" questions?

We have a few tweaks:

  • Succeeding questions from the same site are penalized by increasing amounts. So, the first question from SO in the list gets multiplied by 1.0, the second by 0.98, the third by 0.96, etc)

  • We make a per-site traffic adjustment so SO does not dominate the entire list

  • The benefit of many answers is capped at 10

  • We only degrade based on question age, and not the last update date on a question, so questions don't pop back up to the top every time they're edited

  • Views are not counted towards the score

The core of the formula (without the site-based degrading or traffic scaling) is:

(MIN(AnswerCount, 10) * QScore) / 5 + AnswerScore
         MAX(QAgeInHours + 1, 6) ^ 1.4
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David, one of comments here mentions that this question (and your answer?) is "no longer relevant". Could it be so? in particular, do tweaks you mention still apply to hot questions listed at collider? – gnat Oct 1 '13 at 10:24
@gnat This answer is still correct. The collider uses the same algorithm as the Stack Exchange hot question list. – David Fullerton Oct 1 '13 at 12:20
gnat Actually, it was slightly out of date. See the updated answer. – David Fullerton Oct 1 '13 at 12:57
David, can you please confirm the change regarding the top 3 answers being counted or not? I'd like to rerun my analysis, but I want to make sure I'm using the correct formula. – GlenH7 Oct 8 '13 at 14:34
@GlenH7 We no longer treat top 3 answers specially. All answers are included in AnswerScore – David Fullerton Oct 8 '13 at 14:44
gentle 2% penalty for same-site-questions is easily overruled by stuffing more answers into these, as demonstrated by recent example of 4 math questions occupying top of collider. Dropping tiny 2% when QScore is blindly multiplied by AnswerCount straight up to 10 answers looks futile – gnat Nov 8 '13 at 10:34
"per-site traffic adjustment so SO does not dominate" -- for the record, this is explained in more details in “SO questions are penalized” in the hot list - how does that work, can it be done for other site(s)? – gnat Mar 24 '14 at 12:01
Just to be clear: Are downvotes also counted in AnswerScore? Say, if one answer has 20 upvotes and 5 downvotes, would it have a score of 20 or 15? – Amal Murali May 18 '14 at 7:38
@Amal Yes, both scores are equal to upvotes - downvotes (same thing you see next to the post). If one answer has 20 upvotes and 5 downvotes, the score would be 15. – David Fullerton May 19 '14 at 14:14
@DavidFullerton, So is it right to say that the algorithm is not identifying "hot questions" (as it is named) but "hot answers"? – Pacerier Oct 3 '15 at 10:41

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