Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I even say who wrote them. If you have more recent summaries to add to this collection, send them my way I guess. Sorry for the ads; they cover the costs of keeping this online.
Crosier. 2003. John Snow: The London Cholera Epidemic of 1854. from course CD, originally from a web site..
If nature gives us a natural experiment, how do we know whether it is roughly random? (1) the subjects don't know which group they were assigned to, (2) we don't either. The cholera experiment looks close enough to this test.
Research on similar subjects