In statistics, ignorability refers to an experiment design where the method of data collection (and the nature of missing data) do not depend on the missing data. A missing data mechanism such as a treatment assignment or survey sampling strategy is "ignorable" if the missing data matrix, which indicates which variables are observed or missing, is independent of the missing data conditional on the observed data.
Pearl  devised a simple graphical criterion, called back-door, that entails ignorability and identifies sets of covariates that achieve this condition.
- Ignorability in Statistical and Probabilistic Inference by Manfred Jaeger
- Andrew Gelman, John B. Carlin, Hal S. Stern and Donald B. Rubin. Bayesian Data Analysis. Chapman & Hall/CRC: New York, 2004.
- Judea Pearl. Causality: Models, Reasoning, and Inference. Cambridge University Press, 2000.