[diogenes4]

> I’ve never heard someone use the word arbitrary to mean anything other than “a random choice”, or even “a poorly thought-out choice”.

That's shocking, I use it to mean "the result of a judgement or decision" about a dozen times a day, such as "it's not random, it's arbitrary". I had no clue people had an alternative definition for it. I'm even more surprised that otherwise ostensibly-educated people have no clue about the traditional definition.

[burkaman]

Can you find any recent dictionary with your definition, or modern printed example of the word used in this way?

Etymonline cites a 1640s dictionary with the present-day definition: https://www.etymonline.com/word/arbitrary

[diogenes4]

> Can you find any recent dictionary with your definition, or modern printed example of the word used in this way?

sure, https://www.wordnik.com/words/arbitrary: "Based on or subject to individual judgment or preference." is the second definition on the page. You clearly didn't even bother googling.

Regardless, I'd argue that arbitrary as distinct from "random" only has one definition—the one where judgement, choice, or preference is exercised. This is the useful way to use the word, hence my shock. Especially in a technical context where the connotation of petty abuse of judgement makes no sense.

Finally, there are cases where it's indistinguishable from arbitrary. For instance, if you're defining a pure computation on some integer, the distinction between arbitrary and random is meaningless.

Throwing the word away (as I interpret your sentiment to argue for) seems like the worst possible interpretation and just as likely to lead to confusion.

[burkaman]

I don't think it means quite the same thing as random.

"The judge is giving out random sentences" means the judge is rolling a die or something, literally randomizing each sentence.

"The judge is giving out arbitrary sentences" means the judge is sentencing based on how they feel in morning, or the opinion of the last person they talked to. The decisions are not random, but they aren't based on any coherent set of rules or logical framework. The judge could have made a different decision and it would have made just as much (or just as little) sense.

Another common usage is calling something an "arbitrary distinction". For example, skyscrapers are often defined as buildings that are at least 100 meters tall. That is an arbitrary distinction, in that there is no significant difference between a 99 meter and 101 meter building. It's obviously not random, it was picked because 100 is a nice round number, but when we say it's arbitrary that means we could have drawn the line at any other number and it would have worked fine. In fact, some people define skyscrapers as being at least 150 meters tall, and there is no logical reason that either of these number are better. They are both arbitrary, and saying that "your 23-story building is a high-rise but my 24-story building is a skyscraper" is making an arbitrary distinction.

So back to Nate Silver's quote:

> I don’t think it’s quite right to say these decisions are arbitrary. Ideally they’ll reflect a statistician’s judgment, experience and familiarity with the subject matter.

If these decisions were arbitrary, that would mean the statistician isn't making educated choices. They're thinking "I just saw a cool article on this regression technique, let me try that", or "my favorite programming language is good at X technique", or "I've been wanting to practice Y technique". When asked why they made a particular decision, the statistician might not have a logical explanation.

If the decisions are not arbitrary, that would mean that other statisticians are likely to agree with the decision, or at least understand the logic behind it.

[uoaei]

If I heard someone say that I would think they're making the point only that it was based on personal whim and not pure statistical chance. I wouldn't interpret it to mean that the person's whims are in any way reasonable, just that they're theirs.