Multi-level modeling for understanding DEADLY RADIOACTIVE GAS

Ok, this episode is only sort of about DEADLY RADIOACTIVE GAS. It's mostly about multilevel modeling, which is a way of building models with data that has distinct, related subgroups within it. What are multilevel models used for? Elections (we can't get enough of 'em these days), understanding the effect that a good teacher can have on their students, and DEADLY RADIOACTIVE GAS.

Relevant links:
http://www.stat.columbia.edu/~gelman/research/published/multi2.pdf