Stan - this is a legitimate and interesting question. I don't know of good, representtive, quantitative data that's directly relevant.
However, I can share some experiences from teaching EA content that might be illuminating, and semi-relevant. I've taught my 'Psychology of Effective Altruism' course (syllabus here), four times at a large American state university where the students show a very broad range of cognitive ability. This is an upper-level undergraduate seminar restricted mostly to juniors and seniors. I'd estimate the IQ range of the students taking the course to be about 100-140, with a mean around 115.
In my experience, the vast majority of the students really struggle with central EA concepts and rationality concepts like scope-sensitivity, neglectedness, tractability, steelmanning, recognizing and avoiding cognitive biases, and decoupling in general.
I try very hard to find readings and videos that explain all of these concepts as simply and clearly as possible. Many students kinda sorta get some glimpses into what it's like to see the world through EA eyes. But very few of them can really master EA thinking to a level that would allow them to contribute significantly to the EA mission.
I would estimate that out of the 80 or so students who have taken my EA classes, only about 3-5 of them would really be competitive for EA research jobs, or good at doing EA public outreach. Most of those students probably have IQs above about 135. So this is mostly a matter of raw general intelligence (IQ), and partly a matter of personality traits such as Openness and Conscientiousness, and partly a matter of capacity for Aspy-style hyper-rationality and decoupling.
So, my impression from years of teaching EA to a wide distribution of students is that EA concepts are just intrinsically really, really difficult for ordinary human minds to understand, and that only a small percentage of people have the ability to really master them in an EA-useful way. So, cognitive elitism is mostly warranted for EA.
Having said that, I do think that EAs may under-estimate how many really bright people are out there in non-elitist institutions, jobs, and cities. The really elite universities are incredibly tiny in terms of student numbers. There might be more really smart people at large, high-quality state universities like U. Texas Austin (41,000 undergrads) or U. Michigan (33,000 undergrads) than there are at Harvard (7,000 undergrads) or Columbia (9,000 undergrads). Similar reasoning might apply in other countries. So, it would seem reasonable for EAs to consider broadening our search for EA-capable talent beyond super-elite institutions and 'cool' cities and tech careers, into other places where very smart people might be found.
I shared this idea pretty strongly a few years back, but have changed my mind due to personal experience of running an organisation with lots of people. I think a community has enough parallels for it to be a useful comparison.
Here's what changed my mind:
1. The number of one-to-one relationships increases with the factorial of the number of people in a group. Shit gets complicated and it creates a breeding ground for bad behaviour; you can behave horribly and then move on to a new group of people without facing ramifications, because it's unlikely that those two groups are talking to one and other.
2. At least within an organisation, having a lot of people necessitates hierarchy which itself has major drawbacks e.g. it increases the links in the Chinese whisper chain that is organisational communication, affecting information flow both on the way up and on the way down.
3. You'd think that the productivity of a team would be n * average productivity, but it's more like n * productivity of the worst person; mediocre people lower the standards people hold themselves to and higher performers leave in disgust. New hires then conform the ever lowering standard.
4. A lot of processes are at least somewhat serialized. You can't make them go faster by increasing the number of people, only increasing the quality will move the needle (e.g. a team of 100000 sprinters will still reach the finish line slower than Usain Bolt)
5. A person is smart. People are stupid. When you have large groups, reputation starts to become decoupled from reality. Rumor becomes the dominant mode of information transfer. People start having very strong opinions about people they've barely met or interacted with.
6. The importance of work is power-law distributed. The top priority is usually more important than the tenth through to the nth combined. What really matters is nailing the most important stuff.
Thanks for sharing!