- "In prediction tasks, BART's flexibility is a pure advantage. It finds patterns we didn't know to look for, captures complex interactions automatically, and often achieves superior out-of-sample accuracy. But in causal inference, this same flexibility becomes a liability when it absorbs the variation we're trying to causally attribute. The problem is **structural**: any sufficiently flexible method faces this challenge. Methods that can perfectly adapt their functional form to training data will inadvertently learn causal pathways as associational patterns, unless the structure learning is constrainted to partial out the treatment influences. The stronger the relationship between the predictors of the outcome and the treatment, the more we can expect to see this collapse. Flexible outcome modelling may be useful in cases where the relationship between treatment and covariates is truly independent, but it presents a risk where the focus is on recovering treatment effects."
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