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Quite often I came across questions that ask for a specific thing. More often, the answer is a simple "NO". Something like this does not exist. The dilemma here is it is difficult to prove / establish / evidence something is not there. I could be that I [person who wants to answer] does not conclusively know something like this is not there.

For example How can I hedge against local home value? Well there isn't any such product because the market is small. But then maybe some vague small company / practise somewhere offers it.

There are other such questions;
Historical day-to-day prices for all mutual funds (best if through an API)
Financial product with high variance, instead of lottery
tracking dividend payments automatically

Some similar question have been essentially answered an elaborate NO. For example;
How to determine a reasonable rate of inflation assumption for long-term care?
Are there mutual funds that invest in specific groups of companies?
Australian superannuation funds holding bitcoin?

So the question essentially is as a community how do we go about such questions. Should we leave it open or make an educated assumption / guess and say NO.

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    You generally can't prove a negative assertion, since there might be one exception somewhere in the statistical universe. That doesn't mean we can't answer with a negative if we know of no such case. If someone else does have a verifiable instance, we can clean up later, but until then a consensus "no" is entirely reasonable. – keshlam Dec 22 '16 at 17:08
  • @keshlam " generally can't prove a negative assertion ..." that is the crux of question. – Dheer Dec 23 '16 at 3:45
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There are a lot of questions where the assumptions of the OP are wrong, so "no" with some explanation of why is appropriate. I only tend to answer these questions if I think that others may have similar misconceptions and that it will benefit more than the OP.

I also have a tendency to take a contrarian stance when I think there are views that aren't fairly represented by the OP or other answerers. One of my favorite was: How are stock buybacks not considered insider trading? Obviously the down-voters disagreed with my answer, but I think it was a reasonable viewpoint to add to the discussion.

I think it's okay to let the questions languish or close them if they are not suited to the QA format. I also think it's okay to take the initiative even if you can't prove the non-existence of something. Maybe by ignoring them we leave the site with worse statistics than if we answered or closed them all, but I'm not too worried about the health of our site.

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Here is how I like to handle those questions. If I am quite sure that the answer is "no, it doesn't exist," I'll do some searching to see if I'm mistaken. Then I'll wait a while, to see if someone else knows of an example that I'm not aware of. After some time passes with no examples, and I am still sure that it doesn't exist, I have posted a "no" on these types of questions before. (Here is a recent example on Sports.SE.) For this to be a good answer, however, besides the "no, doesn't exist," the answer should include some sort of explanation: a justification or reason why it doesn't/can't exist.

That having been said, if the subject matter is something I am not very familiar with, I won't post a "doesn't exist" answer simply because I couldn't find it in a Google search. There are lots of things that are difficult to find on Google. I'll let someone with much more expertise answer that one.

In my opinion, if no one wants to stick their neck out and say that it doesn't exist, there is nothing wrong with leaving the question unanswered. In fact, this is probably better than having a short "doesn't exist" answer with no further explanation. Anyone reading the question in the future and seeing that there is no answer will reasonably conclude that perhaps it doesn't exist.

Either way, as long as the question stays open, if someone comes along in the future with a good example (new things are created all the time), they will be able to post an answer. For this reason, I think it is a mistake to close questions like this just because it is believed that the answer is "No." If we answer the question as "no" and close it, it cannot be updated in the future if things change, and can become bad information on our site.

In this discussion, I also think it is important to differentiate between an on-topic question of this sort and a product or service recommendation question, which is off-topic (see this meta question for discussion). I'm not advocating leaving product recommendation questions open, but I think that there can be on-topic questions of the sort we are talking about here that should be left open.

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