Adaptive Private-K-Selection with Adaptive K and Application to Multi-label PATE

Abstract

We provide an end-to-end Renyi DP based-framework for differentially private top-k selection. Unlike previous approaches, which require a data-independent choice on k, we propose to privately release a data-dependent choice of k such that the gap between k-th and the (k + 1)st "quality" is large. This is achieved by a novel application of the Report-Noisy-Max. Not only does this eliminate one hyperparameter, the adaptive choice of k also certifies the stability of the top-k indices in the unordered set so we can release them using a variant of propose-test-release (PTR) without adding noise. We show that our construction improves the privacy-utility trade-offs compared to the previous top-k selection algorithms theoretically and empirically. Additionally, we apply our algorithm to "Private Aggregation of Teacher Ensembles (PATE)" in multi-label classification tasks with a large number of labels and show that it leads to significant performance gains.