I was always puzzled by how disproportionate this chart is. What would be the reason for the top boards to have this ratio over 1000% higher than the bottom ones?
Do they have more active merit sources, or is it more about cultural differences and stronger in-group preferences than the others? Or maybe both.
By far the most important factor is how many active merit sources local board has, and after that is probably how clean of spam board is and quality of the members writing there.
My local board (Croatian) used to have one of the lowest merit/post ratios despite the fact that we didn't have spam at all and posts were generally of a good quality (for example our local board had 4 members in CM campaign, afaik more than any other local board). Only after theymos gave us 2 new merit sources our ratio started going up and now its among the highest of all local boards.