2021
DOI: 10.1007/s11222-021-10057-z
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Unrestricted permutation forces extrapolation: variable importance requires at least one more model, or there is no free variable importance

Abstract: This paper reviews and advocates against the use of permute-and-predict (PaP) methods for interpreting black box functions. Methods such as the variable importance measures proposed for random forests, partial dependence plots, and individual conditional expectation plots remain popular because they are both model-agnostic and depend only on the pre-trained model output, making them computationally efficient and widely available in software. However, numerous studies have found that these tools can produce dia… Show more

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Cited by 120 publications
(66 citation statements)
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“…Since PD plots extrapolate to potentially unobserved areas in the predictor space, they have been critized for being unreliable when predictors are correlated (Apley & Zhu, 2016;Hooker et al, 2021;Molnar, 2019;Molnar et al, 2020;Scholbeck, 2018). Therefore, we will look into the effects of correlated predictors on PD curves further below.…”
Section: Partial Dependence Plotsmentioning
confidence: 99%
“…Since PD plots extrapolate to potentially unobserved areas in the predictor space, they have been critized for being unreliable when predictors are correlated (Apley & Zhu, 2016;Hooker et al, 2021;Molnar, 2019;Molnar et al, 2020;Scholbeck, 2018). Therefore, we will look into the effects of correlated predictors on PD curves further below.…”
Section: Partial Dependence Plotsmentioning
confidence: 99%
“…, X p )]. As argued for example by Kumar et al (2020) and Hooker et al (2021), care is needed in applying and interpreting feature-wise influence metrics as they may rely on the fitted model extrapolating beyond the sample support.…”
Section: Interpreting Individual Featuresmentioning
confidence: 99%
“…However, if the features are correlated, it is possible that the orderings may be biased or that permutations of one feature might result in unrealistic combinations of features and hence would cause the model to extrapolate performance [53]. For example, if all students who earned perfect scores on the physics GRE also had high GPAs, permuting GPA could cause there to be cases where a perfect physics GRE score goes with a low GPA, which would be outside of the region learned by the model.…”
Section: The Random Forest Algorithmmentioning
confidence: 99%