Name the most credible measure of idea production that isn't at least moderately positively correlated with population.
I think this is a somewhat imprecise formulation. First of all, "moderately positive" is vague. It could be a very low bar.
But what is the relevant boundary for measuring population? The nation-state? So if 10 million people are spread over a large area that means the same thing as if they are concentrated on an island? Or if 10 million people speak 8 different languages that is the same thing as if they all speak the same language?
If you look at population at a nation-state level, then any simple linear correlation is bound to be dominated by India and China. If you instead choose a more robust measure, such as rank correlation, you may see different results.
The classic example suggesting less than perfect correlation between population and ideas would be Israel vs. the Arab countries in Nobel Prizes in science. I think it is a striking example, even though it might not be enough to offset a "modestly positive correlation" overall.
I suspect that communication is a huge factor in idea generation and propagation. I would rather have a small population of people who travel and communicate broadly than a large population of people who stay in their villages their whole lives and rarely communicate with outsiders.
But I go back to my original thought, which is that I would like to see some more thought put into coming up with something more precise than "moderately positive correlation" and also a more precise definition of what constitutes high and low population.