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I was playing around with the Data Explorer and found to my surprise that several posts have received votes before they were created:

  • 67 posts on Stack Overflow have received up-votes, down-votes, and/or favorites before their creation date. About a third of these were just within a week before its creation, but most were several months before with the most extreme having three favorite counts dated 1328 days before its creation date.

  • 7 posts on Math exhibit being favorited before their creation date.

  • 73 posts on Ask Ubuntu have been favorited before their creation date.

For all the sites I have tried running this query, I find posts like these. Curiously, only on Stack Overflow, a lot of posts have been up-voted and down-voted "before time" besides being favorited.

Why do votes cast before the creation date of the post exist? Is it because of migration? If then, shouldn't the creation date be migrated properly as the vote cast dates are? Or is this a bug?

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  • 4
    Probably down to questions being merged, certainly all of the ones that I've looked at so far in the SO list have been merged at some point in their life.
    – JonK
    Commented Aug 22, 2014 at 14:02
  • @JonK That's correct, if you want to make it an answer.
    – Tim Stone
    Commented Aug 22, 2014 at 14:03
  • @TimStone Good to know, but I'm afraid I know very little about the details of the merging process. I'd prefer if someone else were able to provide a more authoritative description of why it happens in that way - I'd just be guessing. It was sort of a guess on my part if I'm honest!
    – JonK
    Commented Aug 22, 2014 at 14:06
  • Note that your date calculation doesn't take into account the time of day a question was asked, so can discount anything that has a -1 'age' column.
    – Martijn Pieters
    Commented Aug 22, 2014 at 14:25
  • Related: Why do some comments and responses have timestamps earlier than those for the corresponding question?
    – 3nafish
    Commented Aug 22, 2014 at 18:52

2 Answers 2

Reset to default
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Question posts can be merged; when this happens, not only are answers moved over but all votes are merged as well.

On merging, the dates for the votes are not reset, so you can see votes that predate the target newer question.

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  • Several posts have up-votes and down-votes before their creation date. Are these moved as well?
    – dwitvliet
    Commented Aug 22, 2014 at 14:08
  • What happens reputation wise for the two people that asked the merged questions? Does one lose reputation equivalent to the score of the question that ends up merging into the other one, and does the author of the target then gain any reputation?
    – JonK
    Commented Aug 22, 2014 at 14:09
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    @JonK no; our voting data includes a TargetUserId - we explicitly record the target user separately to the target post.
    – Marc Gravell
    Commented Aug 22, 2014 at 14:12
  • @Banana: looks like this applies to votes as well; this example has upvotes 140 days before the question date, and the age of the answers certainly shows the question was merged.
    – Martijn Pieters
    Commented Aug 22, 2014 at 14:12
  • @MartijnPieters Wauw, you're right, the answers were posted "before" the question. Why isn't the creation date of the question just taken from the oldest post? How it is now is very confusing.
    – dwitvliet
    Commented Aug 22, 2014 at 14:16
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    @Banana That would make the dates inaccurate. Take this one as an example - it was posted on May 25 '12 at 17:42, not Oct 16 '10 at 21:56, which is when the mergee was posted. To say otherwise would be wrong, and would raise the possibility of a user appearing to have asked a question before their account had been created instead.
    – JonK
    Commented Aug 22, 2014 at 14:24
  • @MartijnPieters This was helpful. Is it then safe to assume that any positive difference between the creation dates of Answers and Questions would refer to questions that have simply NOT been merged? Is there anything else that can lead to Answers before Questions?
    – A_A
    Commented Dec 29, 2015 at 23:55
  • @A_A: merges can go the other way too; a newer post merged into an older. That leaves a positive difference between the dates of the answers and the question. I'm not aware of any other way answers can end up predating the question, no.
    – Martijn Pieters
    Commented Dec 30, 2015 at 0:07
  • @MartijnPieters Thanks for such a quick response. Then, the only way of telling a merge is by examining the TargetUserId? (BTW, Is there somewhere a document explaining the schema and these discrepancies that may be encountered?)
    – A_A
    Commented Dec 30, 2015 at 0:32
  • @A_A: Only Database schema documentation for the public data dump and SEDE exists. There are no discrepancies, only peculiarities as to how the site works. The latter is not centrally documented, it is experience and observation and reading loads of posts here that brings that knowledge.
    – Martijn Pieters
    Commented Dec 30, 2015 at 0:48
  • @MartijnPieters This is already a better start than nothing. Thank you very much. Peculiarities indeed, sorry for demoting to "discrepancies" :)
    – A_A
    Commented Dec 30, 2015 at 1:00
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Merged questions, basically. For example, 75189 on meta:

enter image description here

Sometimes, when questions are merged, the newer question is kept as the master; the transferred votes / favorites / etc retain their original dates, however.

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  • Presumably adding entries in the history is a relatively 'recent' addition; this question clearly is a merge, but there is no entry in the history indicating what was merged with it.
    – Martijn Pieters
    Commented Aug 22, 2014 at 14:18
  • @MartijnPieters yes, I agree; nothing explicit in the history of that one. There's a flag dated Aug 1 '09 suggesting the merge, so it probably happened then. So we have a time-frame of Aug 2009 to Aug 2011 for when we improved the recording of merges.
    – Marc Gravell
    Commented Aug 22, 2014 at 14:21
  • I can narrow that window to July 2010 at the latest.
    – Martijn Pieters
    Commented Aug 22, 2014 at 15:16

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