I've noticed some extremely un-hot mathematics questions pop up on the hot network questions list. Low number of upvotes, only one answer, etc. Even odder, there's always at least one MathOverflow question on the list, when I rarely recall ever seeing any before. Am I just imagining this or did something change?
Case in point. Nobody cares about this question. But it's on the list.
A few weeks ago, I was curious about whether the famous formula would still hold. Note that the formula itself does not mention three site specific penalties, and there's a mysterious traffic factor. Therefore, I've expanded my HNQ scraper with some API calls to fetch some relevant variables for the score. Today's traffic (visits/day) was obtained from the Sites list. The collected data can be downloaded from GitHub; you'll need the HNQ.backup made with PostgreSQL 9.4 to do some analysis yourself.
If we look at the Hot Network Question list of November 8th, 23:45 UTC, and calculate the score manually with the formula linked above, we see that the results are quite different (the first 12 rows are shown below):
site question hotness calc_hotness multiplier views traffic
----------------------------------------------------------------------------------
history 49243 161.908 4.498611027 35.99066446 5873 12954
codegolf 175485 122.779 3.653743744 33.60361552 1479 5854
security 197236 118.193 3.280403085 36.03002342 3394 65844
workplace 122351 95.202 3.536535567 26.91956525 2304 43644
writing 39988 94.765 2.627507326 36.06650268 2106 10607
worldbui... 129621 87.784 2.116223815 41.4814347 604 16364
space 31898 79.908 2.213475868 36.10068722 2418 8506
math 2990086 77.972 2.209022054 35.29706725 724 368175
rpg 135174 72.919 2.020590163 36.08797139 2021 65265
security 197250 68.433 2.535478516 26.99017151 1851 65844
puzzling 74890 61.784 1.481356671 41.70771377 508 13375
While the hottest questions have a score of about 100, the calculated scores don't even reach 5 (the Workplace one 6.4, but it's penalized.) Also, while there's a general tendency of the calculated scores to go down together with the 'real' hotness, the factor (multiplier) can be as high as 44.5 and as low as 13.5. (The penalty for multiple successive questions from a site is not calculated, but for the top questions it can't be more than a few percent). The traffic does not seem to play any role for the multiplier; Space and Writing get the same multiplier as the 1st Security question and RPG, even though their traffic is 6-8 times less. Also, Mathematics doesn't seem to have a particularly high multiplier, and neither does MathOverflow (it's not in this list but I've checked a few other questions).
Moreover, the multiplier doesn't seem to be constant over time, not even for a single site or even question. Let's take the top question in the previous list, #49243 from History:
timestamp hotness calc_hotness multiplier views traffic
-----------------------------------------------------------------------
2018-11-08 23:45 161.908 4.498611027 35.99066446 5873 12954
2018-11-08 23:30 161.908 4.498611027 35.99066446 5803 12954
2018-11-08 23:15 161.908 5.213614673 31.05484585 5740 12954
2018-11-08 23:00 179.417 5.213614673 34.41316845 5663 12954
2018-11-08 22:45 176.217 5.065972488 34.78443683 5597 12954
2018-11-08 22:30 169.817 4.927557939 34.46270995 5493 12954
2018-11-08 22:15 169.817 5.7565156 29.49996349 5407 12954
2018-11-08 22:00 200.258 5.70210619 35.12000537 5293 12954
2018-11-08 21:45 200.258 5.70210619 35.12000537 5177 12954
2018-11-08 21:30 196.448 5.647696779 34.7837371 5037 12954
2018-11-08 21:15 192.258 6.664329354 28.84881431 4914 12954
2018-11-08 21:00 219.856 6.533141768 33.6524153 4792 12954
2018-11-08 20:45 217.634 6.467547975 33.65015626 4678 12954
2018-11-08 20:30 210.967 6.336360389 33.29466555 4552 12954
2018-11-08 20:15 206.523 7.618405734 27.10842756 4433 12954
2018-11-08 20:00 257.428 7.830028116 32.87702115 4321 12954
2018-11-08 19:45 257.428 7.830028116 32.87702115 4179 12954
2018-11-08 19:30 231.294 7.113767747 32.51357202 4040 12954
2018-11-08 19:15 228.628 6.9509813 32.89147102 3914 12954
2018-11-08 19:00 282.451 6.869588076 41.11614799 3782 12954
Some of those discrepancies can be caused by caching; hotness scores are cached and my scraper fetches these data only after reading the HNQ list. But I wouldn't expect it to fluctuate so much for a single question; also, there are other questions from History where the multiplier stays in the low 20s (even though they were the highest scoring History questions at that moment).
Conclusion: I can't tell whether there is a new algorithm (for that, we would need data from previous periods as well) but the formula isn't telling us everything.
MAX(QAgeInHours + 1, 6) in the post you refer to doesn't quite fit my observations. You could try 7 or 8 instead of 6 there. Or maybe even harder modification, like constant 1 when age is less than 8 hours changing to QAgeInHours for questions older than 8 hours, this seems closest to what I feel observing the HNQ