They can be correlated without being a tight linear relationship. If every two people in a group have exactly one transaction, then adding 20 people to a group

They can be correlated without being a tight linear relationship. If every two people in a group have exactly one transaction, then adding 20 people to a group of 100 will create more new transactions than you'll find in a group with just 20 people. To be fair, when I google for research on correlations between economic growth and population growth, I get a jumble of papers on opposite sides - some pro-natalist and some anti-natalist and some agnostic. (Maybe one camp is considered far more authoritative than the others?) Maybe it's a nontrivial relationship if it exists, though I'm not convinced anyone knows definitively how the relationship plays out.