Reader question — Causal claims when you cannot randomise

Reader question on Causal claims when you cannot randomise, and the answer belongs somewhere more findable than an email.

Half the interesting questions cannot be tested. Here is what is available instead, what each method assumes, and how to state a conclusion you can defend.

The question was, roughly, "when does this stop applying?" — which is the right question and the one lessons routinely fail to answer. Every technique has a range of validity, and stating it is what separates a lesson from a recipe.

It sits in the Experiments and causal claims module. The exercise is a thinking one rather than a query one — some of this material is about deciding what to compute, and that does not need a keyboard.

Ordering matters here more than in most courses. It follows Reading a result without fooling yourself and leads into Frame the problem, then beat a stupid baseline, and reading it out of sequence mostly works but costs you the setup.

Free means free, and it also means we can rewrite it whenever it is wrong. No edition, no errata PDF, nothing to repurchase. The whole course is 36 lessons and the fixes land the day we find them.