Figure 1 is clumsy, sorry. In the case of a smooth probability distribution of infinite worlds, I think the median and the average world are the same? But in practice, yes, it's an expected value calculation, summing P(world) * P(U|world) for all the worlds you've thought about.

Good q, yes, that's the vertical axis in all the figures.

This is so awesome and encouraging! I play old-time fiddle and I've wanted to play dances for years, but I've been afraid I can't get enough tunes up to dance tempo. But I can play a lot of the tunes on your list! You've given me the push I need. Thanks Lily and Jeff! Sounds like a lot of fun.

Thanks for this, Jeff! I'm planning to have two MERV-14 cubes going at an upcoming contra-dance. I'll refer curious people to this post.

I couldn't find 20x20x1 filters at my local hardware store; only 20x14x1 and 20x30x1. I don't have a good intuition for how effectiveness relates to filter size. How much less effective do you think a 14-inch tall "cube" would be than a proper cube?