When is "primarily opinion based" a valid reason to close?

Question

In my new capacity to close vote without undue weight, I feel the need to revisit a previous question about the close reason, "Primarily Opinion Based".

How does one know what one doesn't know?

I don't want to insult anyone, but We Are All Confident Idiots* (and I am no exception) is an interesting read, and would make for some potentially beneficial required reading before voting (or answering) on any SE site.

The problem I see in voting to close due to POB is that a vast amount of information exists on almost every aspect of human health. Just because someone doesn't know how to search the database doesn't mean the answer (with evidence to support it) isn't out there.

An example: Can ingesting a mosquito make you sick? The answer to this (with reference to HIV specifically) is not Primarily Opinion Based. The research on risk of acquiring HIV from various exposure modalities is more than encyclopedic. Risk of acquiring the infection from ingestion is certainly available. That means there's fact-based evidence for an answer. (You - or I - may not want to answer it, or may think it's a trivial question, but it's not POB.)

https://health.stackexchange.com/q/4217/169 is not Primarily Opinion Based. It might be unclear what the OP is asking, but the literature on bone structure variation (especially in physical anthropology) is vast.

I've seen questions closed on another site as POB which I know has an evidence-based answer. The problem is that people who don't know that studies have been done on something they're unfamiliar with think it's POB.

I'm not saying that people can't close questions as POB. But I'm wondering: can we come up with guidelines for deciding if a question is POB or just a head-scratcher?

*_{A quote: Because of the way we are built, and because of the way we learn from our environment, we are all engines of misbelief. And the better we understand how our wonderful yet kludge-ridden, Rube Goldberg engine works, the better we — as individuals and as a society — can harness it to navigate toward a more objective understanding of the truth.}

Answer 1

Because you're asking for guidelines, I'll try to write one which is easily applied to any question:

Imagine a continuum from "Answer requires a human judgement based on the person's values and preferences" to "Science should be able to find an answer which is objectively true or false". The closer to "requires human judgment", the more likely that it's POB.

As an example for clearly opinion based: "Which color is more beautiful, blue or yellow?". Example for clearly not POB: "What is the height of Mont Blanc over sea level?".

"Has science already found out the answer" is not important. What is important is the nature of question as it relates to matters of fact vs. matters of taste.

Note that sometimes a question may look very objective to a confident idiot, but turn out to be entirely subjective. This usually comes from people who honestly assume that a cultural practice which happens to be universal to their society is universal to all humanity and predetermined by some natural law. "Why are eggs only suitable for breakfast?" would be such a question, containing the assumption that eggs are no good outside breakfast - a statement which might be presumed true by many people in the US, but obviously false.

I would also go so far to suggest that "there's no actual problem" and "they attract lots of answers" from Shog9's answer are not necessary conditions for declaring a question to be POB. Sure, these sings turn up in lots of POB questions, but a question can be POB without having them.

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I'll also try to apply my logic to the two examples you mentioned:

1) HIV infection through mosquitoes: clearly not POB. Even if nobody had found it out yet, it should be obvious that there is a clear "yes" or "no" answer which is knowable in principle.

2) Big boned. That one's tough. If the question is about relation of bone size to body size, then certainly not POB. But "big boned" is a set term in our society which has very complicated connotations. If the asker actually wanted to understand if "I am big boned" can be true or is always a lie, that depends on a human's judgement of what the term is actually supposed to mean, how relevant its literal, physiological meaning is to the conveyed meaning, and what constitutes a lie. So it's not clear cut. I would tend to say it should be open, but the OP should be advised in comments that he will only get physiologically relevant answers, and that they may not contain the information crucial to understanding the term's usage in nonmedical contexts.

Answer 2

"Primarily Opinion Based" references something that... Actually doesn't show up all that often on Stack Exchange sites, but is something of a staple of most other forums and Q&A sites. A visit to Quora's Health topic turns up a few examples:

• What are the best ways to lose weight?
• What are the top 5 must do and don't do for depressed people?
• What are some female habits in the wash room that men don't know about?

Checking the FAQ for that topic quickly yields a few more:

• Where do I get advice for health issues online?
• What are some home remedies to remain healthy and fit?
• What is the best way to get reliable health advice?

There are some reasonable answers lurking within these questions, but a number of problems quickly become apparent:

• There can be no "right" answer to any of them. Plenty of questions have multiple correct answers, or answers that only apply in certain situations... But a question where any possible answer is likely as correct (or incorrect) as any other is another beast. This can be considered an extreme case of Too Broad; if answering a Too Broad question might require an entire textbook, then answering one of these questions might require an entire library: stacks, periodicals, microfilm copies of newspapers with letters to the editor from crazy hermits crediting their longevity to a daily diet of Sterno and talk radio...
• There's no actual problem. Maybe there's a token nod to a general problem (lots of people do need to lose weight), but even that isn't required; the call is out for responses more than solutions. These could also be classified as Unclear, but often they are clear: they want responses and opinions, as many as possible. Which brings us to...
• They attract a LOT of answers. Again, there's nothing wrong with multiple solutions to a problem, or multiple approaches to an explanation. But usually this peters out after a reasonably small quantity, resulting in a set of answers that can actually be read and used by the asker and future readers. Once you start seeing dozens or hundreds of answers, the chance that anyone is going to read them all is slim; voting becomes ineffective, and if there is anything of value it becomes lost in the noise. Spam and trolling grow and fester in the moist recesses...

Oh... And both because of the broad appeal and low barrier to entry, these questions are often incredibly popular. That they aren't usually a problem here is a testament to the battles fought early on over their suitability for this Q&A format; early threads on Stack Overflow often followed the same patterns illustrated by the questions above, and their downfall resulted in a widespread reluctance to see new sites suffer through the same growing pains. Every site now includes a Don't Ask topic that explicitly warns about them:

You should only ask practical, answerable questions based on actual problems that you face. Chatty, open-ended questions diminish the usefulness of our site and push other questions off the front page.

Your questions should be reasonably scoped. If you can imagine an entire book that answers your question, you’re asking too much.

If your motivation for asking the question is “I would like to participate in a discussion about ______”, then you should not be asking here. However, if your motivation is “I would like others to explain ______ to me”, then you are probably OK.

This topic also includes some handy checks (borrowed from MetaFilter) to aid in identification:

• every answer is equally valid: “What’s your favorite ______?”
• your answer is provided along with the question, and you expect more answers: “I use ______ for ______, what do you use?”
• there is no actual problem to be solved: “I’m curious if other people feel like I do.”
• you are asking an open-ended, hypothetical question: “What if ______ happened?”
• your question is just a rant in disguise: “______ sucks, am I right?”

If you never encounter a question that suffers from these problems, count yourself lucky - they're annoying, and often deceptively hard to fix compared to similar "too broad" or "unclear" questions. If you think you've encountered one, a quick test is to simply ask the author to clarify the problem he's trying to solve / highlight the bit he doesn't understand / explain where he's stuck. If there's a real question to be had, this'll flush it out...

I'm also gonna call out an excellent answer on the sister site for Skeptics, where Oddthinking lays out the problems with (and solutions to!) a related class of questions there.