Classification under Nuisance Parameters and Generalized Label Shift in
  Likelihood-Free Inference
Luca Masserano Alex Shen Michele Doro Tommaso Dorigo Rafael Izbicki Ann B. Lee
An open scientific challenge is how to classify events with reliable measures
of uncertainty, when we have a mechanistic model of the data-generating process
but the distribution over both labels and latent nuisance parameters is
different between train and target data. We refer to this type of
distributional shift as generalized label shift (GLS). Direct classification
using observed data $\mathbf{X}$ as covariates leads to biased predictions and
invalid uncertainty estimates of labels $Y$. We overcome these biases by
proposing a new method for robust uncertainty quantification that casts
classification as a hypothesis testing problem under nuisance parameters. The
key idea is to estimate the classifier's receiver operating characteristic
(ROC) across the entire nuisance parameter space, which allows us to devise
cutoffs that are invariant under GLS. Our method effectively endows a
pre-trained classifier with domain adaptation capabilities and returns valid
prediction sets while maintaining high power. We demonstrate its performance on
two challenging scientific problems in biology and astroparticle physics with
data from realistic mechanistic models.