So the question becomes: "7, 8, or 9?"
Still some strategy to think about here. If you answer "7", then you're saying, "I'm not that good but even I know not to answer lower than 7". Answering "9" is similar, except you're saying you know better than to go full self-aggrandizement.
Yup. Nothing of value is gleaned from this question.
I recall an amusing HN story from a couple years ago: $candidate was asked about his proficiency with $open_source_program. $candidate was challenged on his not-so-humble answer ...and then suggested that the interviewer compare his name with that of the author/lead maintainer of $open_source_program.
> So the question becomes: "7, 8, or 9?"
I'd throw in a few plausibly-relevant things that zero-ish candidates will have meaningful proficiency at, as an honesty test.
Context matters. Back in 2007, a Google recruiter asked me to rate myself 1–10 on maybe 20 different areas. I gave a bunch of 1–6s, probably a couple 7s, maybe an 8 (don't remember), no 9s or 10s. My interviews focused on the areas I'd self-assessed most highly on, and I got hired.
They set expectations as described in my other comment here: https://news.ycombinator.com/item?id=40907661
Same goes for the 9s or 10s. If it's an area I've truly mastered, then that 9/10 becomes a good starting point for discussion in an area I'm really confident in.