The Napkin problem is an example causality problem, by Pearl, that cannot be solved by the front-door adjustment formula nor the back-door adjustment formula. It argues the need for the more sophisticated do-calculus. Note, however, how it can be reduced to the usual formulae by jointly identifying two variables.
References
- https://stats.stackexchange.com/questions/514615/do-calculus-for-causal-diagram-7-5-from-the-book-of-why-napkin-problem
- Diagrammatic Causal Inference Continued (Piedeleu, 2023), and Structured Probabilistic Reasoning (Jacobs, 2026), for a string-diagrammatic treatment.
- The Book of Why, The New Science of Cause and Effect (Pearl, Mackenzie, 2018)
Tags: causality