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I'm trying to find a possibly deleted question. I don't remember the user. Is this possible?

It was a question about finding $$\operatorname{E}\left[g(X)\right]$$ If my memory serves me correctly $$g(X)=\frac1{1+e^{-(X+c)}}$$ Where $c$ is a constant. Can any of the mods assist? I know for sure that the tags were statistics and expected-value. I did bookmark the question but I guess that deleted questions don't appear on a user's list of bookmarked questions.

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    $\begingroup$ How recently did you view the question? $\endgroup$
    – Sarvesh Ravichandran Iyer
    Jan 7, 2022 at 15:19
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    $\begingroup$ Additionally : deleted questions do remain on the set of bookmarked questions. $\endgroup$
    – Sarvesh Ravichandran Iyer
    Jan 7, 2022 at 15:23
  • $\begingroup$ Definitely within the last four days. $\endgroup$
    – k170
    Jan 7, 2022 at 15:26
  • $\begingroup$ I started working on the question on or after Jan 4th. Then, I could no longer find it. $\endgroup$
    – k170
    Jan 7, 2022 at 15:44
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    $\begingroup$ Your browser history is another likely resource. In this case I can see that the post is in your bookmarks, maybe you can order them by Newest? $\endgroup$
    – hardmath
    Jan 7, 2022 at 15:46
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    $\begingroup$ I mostly use the app so I don't think my browser history will help much. $\endgroup$
    – k170
    Jan 7, 2022 at 15:49
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    $\begingroup$ The author of that post did delete it yesterday. $\endgroup$
    – hardmath
    Jan 7, 2022 at 15:50
  • $\begingroup$ @hardmath, can you confirm if my definition of $g$ is correct? $\endgroup$
    – k170
    Jan 7, 2022 at 15:56
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    $\begingroup$ Got it. The question is : if $X \sim N(\mu , \sigma^2)$, then find a closed form for $\mathbb E(\frac 1{1+e^{-(c+X)}})$. The only context provided is that it is not necessarily true that $\mathbb E[f(X)] = f(\mathbb E[X])$, which is quite straightforward anyway. The question is here, although it is visible only to users above a certain rep. A comment says : "by LOTUS, $\mathbb E[f(X)] = \int_{\mathbb R} f(x) \phi(x)dx$". $\endgroup$
    – Sarvesh Ravichandran Iyer
    Jan 7, 2022 at 16:01
  • $\begingroup$ I'm not able to see the post in my bookmarks when I order it by newest. Is this a special privilege of some sort? $\endgroup$
    – k170
    Jan 7, 2022 at 16:02
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    $\begingroup$ I'm not sure. What I see is this : in this page which is your activity page, if you go down to the bookmarks section, then to the extreme right of the heading "Bookmarks" you will see the sort options "votes/activity/newest/views/added". At least on a PC, I think this is the case. $\endgroup$
    – Sarvesh Ravichandran Iyer
    Jan 7, 2022 at 16:05
  • $\begingroup$ Thank you Sarvesh! $\endgroup$
    – k170
    Jan 7, 2022 at 16:06
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    $\begingroup$ @SarveshRavichandranIyer I think this is the explanation: it you display the bookmarks of this user, you can see the question - since you have reputation 10k+. But this is not the case when a user below this reputation (including the OP) displays the tab with the bookmarks. (There is a related feature request on meta: Users with less than 10K rep can add their own deleted question to favorites but can't see it listed.) $\endgroup$
    – Martin Sleziak
    Jan 7, 2022 at 16:35
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    $\begingroup$ @MartinSleziak I didn't know that, thanks. I mean, I expected the link to be there but the question to be invisible. If it's not in the list at all, then I'm happy I could retrieve it. $\endgroup$
    – Sarvesh Ravichandran Iyer
    Jan 7, 2022 at 16:48
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    $\begingroup$ Side note : LOTUS, is this. $\endgroup$
    – Sarvesh Ravichandran Iyer
    Jan 7, 2022 at 17:31

2 Answers 2

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DISCLAIMER: As you can see, only some of the suggestions I have given below would actually help you to find this specific question. (And some of them only during the next week - after the next update of SEDE.) But at least they are some general suggestions what one might do in similar situations - so even the ones which don't help now might be useful in other instances.

Who can see deleted questions?

Provided you have a link to the question:

  • If you have posted the question or one of the answers - you can see the question.
  • If you have 10k+ reputation points - you can see the question.

So if either of the two possibilities above is true, the only problem is finding a link to the question. If neither of them is true, even with the link you won't see the question. (You might still have some luck that you can possibly find some version of the question in Google Cache or Wayback Machine. Or maybe some of the 10k+ users would be willing to copy the question and the answers for you somewhere, if it can be somehow located.)

See also the FAQ post: How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion? (Specifically, the sections "Can I still see my own post even after it's deleted?" and "When can I see others' deleted posts?")

Who can see deleted questions in various lists?

To the best of my knowledge, this is also restricted to 10k+ users. In this instance, you have mentioned that you have bookmarked the question. If I look at your bookmarks. I can see this question: If $X \sim N(\mu, \sigma^2)$, how to calculate the expected value $E\left(\frac{1}{1+e^{-(c+X)}}\right)$ where $c$ is a constant? (And the same should be true for any 10k+ user.) I assume you don't see the question in your bookmarks. Some other lists work in the same way. (For example, if you look at a list of questions that got some badge, 10k+ users should see also deleted questions there - but not users with lower reputation.)

A possible workaround - to get your bookmarks including the deleted questions from SEDE - is described below.

Relevant posts on Meta Stack Exchange: Users with less than 10K rep can add their own deleted question to favorites but can't see it listed and Are deleted posts shown in badge-related lists?

Users with sufficient reputation can also see the list of recent deletions through moderator tools (a.k.a. 10k tools). However, this list has limited size and does not include self-deletions. (See also: Why are self-deleted posts not shown in the 10k Tools? and Which deletions are not shown in 10k-tools? Are posts deleted by roomba shown there?)

Who can search for deleted questions?

Using the built-in search, only some users might be able to locate deleted posts. Moderators can search among all deleted posts. 10k+ users can search among their own deleted posts. Any user can locate their deleted questions/answers which are relatively recent.Any user can list all their deleted questions and all their deleted answers.1 For details, see: Is there any way to see my deleted questions or answers?

So in this specific case, if either the question or one of the answers was posted by you, you would be able to see it in the list of your deleted questions/answers.

In the case that you have described, this means that if you have 10k+ reputation points and< either the question or one of the answers was posted by you, you would be able to locate it by searching for: [statistics] [expected-value] deleted:1.

How can users with lower reputation try to find deleted questions?

If you are below 10k+ reputation points, the search option described above is not available to you. But still might try other things to locate the link. (But keep in mind that even if you have the link, the post will be displayed to you only if you're the author of the question or one of the answers.)

  • You say that you have viewed the post in the past few days. You might try to look in your browser history for pages/URLs that could be related to your question. (Basically any modern browser keeps your browsing history.)
  • You might try to search in Google - or some other search engine - with restriction on some date range. If you're lucky, you might find the link and see some version of the post in Google Cache. (For example, one could try to search for "expected value" site:math.stackexchange.com and restrict the search results to the last week. (In this specific case, I wasn't able to find the post you wanted in such way. Maybe you might be able to come up with some better search keywords and find it in this way.) EDIT: After playing around with various search phrases, I happened to notice that if I check Google Cache for the newest questions tagged expected-value, I can see this question there. But one should keep in mind that Google Cache will eventually change again.
  • Another option is to use SEDE. You can find some links to useful information about this tool in the corresponding tag-info. For the purposes of this specific situation, it is useful to know that it is a database which contains information about posts on Stack Exchange sites. (And also about users, comments, badges, etc.) The database contains some information about deleted questions - among other things tags. This means that using SEDE you should be able to get links to all deleted questions which had some tag (or set of tags). However, the database is only updated once a week. So if the question you're looking for was deleted very recently, you will only see it after the next update (i.e., after the next Sunday). Various useful queries can be found on meta - for example here: Are there some tools to follow deletions on this site?
  • In this specific instance, you say that you remember two tags. Here is a query which gives links to posts with the two given tags deleted between the two given days. As you can see, I have set up the parameters for the tags and and deletions in December 2021 and January 2022. At the moment, the query returns five links, all of them deleted in 2021. (I went through them and I did not see the question you're looking for.) If the question was deleted between since the last database update (and if the question had those two tags), the link should appear among the results of this search query the next week.
  • You cannot see the question among bookmarks. But the votes table in SEDE also includes votes on deleted questions. So you could try queries such as: List of my bookmarks or a more detailed version of the same query. Again, since you bookmarked this specific question after the most recent update of SEDE, you will only see the link to this specific question there if you try the same query the next week. (But already now you can see that the list contains links to some deleted questions.)
  • EDIT (on January 9): You can check that now - after the SEDE was updated - the three queries mentioned above will, among other things, return a link to this question. (I mean the query showing questions with the two tags and both versions of the query showing your bookmarks.)

How to get to the question if you have a link but it is not displayed on the site?

1This is a relatively recent change. It used to be the case that you would only be able to get through your profile to your deleted posts which were at most 60 days old. I suppose that various places where this is documented will eventually be updated to the current state.

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    $\begingroup$ Very informative post. Thank you for this answer. $\endgroup$
    – k170
    Jan 7, 2022 at 16:11
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Heeding to the request of Martin, I'll reproduce the question verbatim and provide a link to it.

First, a couple of failed attempts. This question wasn't visible in the "recently deleted" section of the mod tools, because it was deleted more than 13 hours ago as of the time of asking the question. Second : it wasn't on SEDE, given that it was actually posted on Jan 3rd (a Monday) and deleted yesterday , while SEDE only updates every Sunday.

On visiting this page, I found to the extreme right of the text (in large font) "Bookmarks", five sorting options, namely votes/activity/newest/views/added. (All this on the "full" site, by the way. I don't know how it works on the mobile site).

I clicked on the "newest" sort option , and this came up. The question had a score of +1, and the comment had a score of 2.I am not aware if the user cannot see this or not, but either way, here's the question.

Title : If $X∼N(μ,σ^2)$, how to calculate the expected value $E\left(\frac{1}{1+e^{−(c+X)}}\right)$ where $c$ is a constant?

Body :

Suppose $X \sim N(μ,σ^2)$. Is there a way to calculate $E\left(\frac{1}{1+e^{−(c+X)}}\right)$ where $c$ is a constant?

Let $f(X) = \frac{1}{1+e^{−(c+X)}}$. I know that $E(f(X))\neq f(E(X))$. Is there a way to calculate $E(f(X))$ in closed form?

Tags : ,

Comment : If $\phi$ is the density function of $X$ then by LOTUS we have $E[f(X)]=\int_{\mathbb R} f(x)\phi(x)dx$.

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    $\begingroup$ Thanks for posting the answer. (I think that it is good that there is an answer dealing specifically with the question the OP was asking about and also an answer with various suggestion that sometimes might help - sometimes not.) As I have mentioned in chat, I only notices the information that the OP bookmarked the question only later - in fact, after posting the first version of my answer. That might be one of the reasons why my answer feels a bit unfocused ... $\endgroup$
    – Martin Sleziak
    Jan 7, 2022 at 18:29
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    $\begingroup$ ... it mentions various possibilities, using the bookmarks was probably the fastest option. (But it is easy to say that now, with the hindsight. - after the question has already been found.) $\endgroup$
    – Martin Sleziak
    Jan 7, 2022 at 18:29
  • $\begingroup$ @MartinSleziak Thanks for requesting me : I think your answer is really nice as well, +1. It's important to be able to search for post-deleted questions in general, because you want to retrieve posts of low quality that may have been deleted but you feel you can ask better. So it's good to have two answers up, one specific and one more general. $\endgroup$
    – Sarvesh Ravichandran Iyer
    Jan 7, 2022 at 18:31

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