Interactive Fingerprinting Codes and the Hardness of Preventing False Discovery
Proceedings of The 28th Conference on Learning Theory, PMLR 40:1588-1628, 2015.
We show an essentially tight bound on the number of adaptively chosen statistical queries that a computationally efficient algorithm can answer accurately given n samples from an unknown distribution. A statistical query asks for the expectation of a predicate over the underlying distribution, and an answer to a statistical query is accurate if it is “close” to the correct expectation over the distribution. This question was recently studied by Dwork et al. (2015), who showed how to answer \tildeΩ(n^2) queries efficiently, and also by Hardt and Ulman (2014), who showed that answering \tildeO(n^3) queries is hard. We close the gap between the two bounds and show that, under a standard hardness assumption, there is no computationally efficient algorithm that, given n samples from an unknown distribution, can give valid answers to O(n^2) adaptively chosen statistical queries. An implication of our results is that computationally efficient algorithms for answering arbitrary, adaptively chosen statistical queries may as well be \emphdifferentially private. We obtain our results using a new connection between the problem of answering adaptively chosen statistical queries and a combinatorial object called an \emphinteractive fingerprinting code Fiat and Tassa (2001). In order to optimize our hardness result, we give a new Fourier-analytic approach to analyzing fingerprinting codes that is simpler, more flexible, and yields better parameters than previous constructions.