First off, you wouldn't need to do that specifically. You'd only need to know that most of the people you talk to are above an 80 IQ on any given topic, in fact most people are about a 100 IQ on any given topic. So you already have a reasonable baseline for comparison.

Secondly, I'd say you're likely the one missing OPs point by trying to take a mostly colloquial statement about how ChatGPT is about as informed as the bottomish X% of the population on any given topic and trying to be pedantic about it. Furthermore the real purpose of OPs point is that the X% is now a lower bound, even if X isn't 16% but 5%, it's only going to go up from here. Yes there's evidence of diminishing returns with the current architectures but there's also a lot of room for growth with newer architectures or multimodal modals.

I think most people understand OPs point without having the need to go around asking everyone what their IQ is. There are numerous indicators, both formal and informal, that indicate that ChatGPT is as informed on most any given topic as the bottom 16% of the population. In fact, it's likely much much higher than that.

I don't think OP's point made much sense in any context.

If you said "Let's talk rocket science" and I said "As a human being I would be happy to help you with that" then everytime you spoke I bluffed my way through the conversation by reciting lines from a Wikipedia article or a library book am I talking like an 80 IQ person, a 100 IQ person, or a 250 IQ person?

What does "converse" "informed" or "IQ" even mean in this context?

Since when does IQ measure the amount of education someone has on a topic, for that matter?

Would a 79 IQ person who has seen the Mary Tyler Moore show converse on it worse than a 200 IQ person who has never watched it?

Is a 200 IQ person reciting a TV Guide article on the Mary Tyler Moore show doing it better than a 79 IQ person doing the same exact thing?

How does one decide if software is "informed" on a subject? Is an encyclopedia "informed" on the world? Is a password manager where I've written my password "informed" about my password? What are we talking about here?

So apparently you have a lot to say about IQ but don't understand the basic fact that IQ isn't a measure of how much someone knows about a topic.

It also isn't a measure of how great it is to have a conversation with someone, for what it's worth.

I agree with you in general, but you are off by using "IQ on the topic". I am almost sure "on the topic" does not make sense for IQ.

IQ of GPT is general in a sense that it can solve novel tasks that some IQ 80 individuals would not be able to as long as the tasks and responses can be encoded in plain English.