Differentially private projected histograms: construction and use for prediction

  • Authors:
  • Staal A. Vinterbo

  • Affiliations:
  • Division of Biomedical Informatics, University of California San Diego, San Diego, CA

  • Venue:
  • ECML PKDD'12 Proceedings of the 2012 European conference on Machine Learning and Knowledge Discovery in Databases - Volume Part II
  • Year:
  • 2012

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Abstract

Privacy concerns are among the major barriers to efficient secondary use of information and data on humans. Differential privacy is a relatively recent measure that has received much attention in machine learning as it quantifies individual risk using a strong cryptographically motivated notion of privacy. At the core of differential privacy lies the concept of information dissemination through a randomized process. One way of adding the needed randomness to any process is to pre-randomize the input. This can yield lower quality results than other more specialized approaches, but can be an attractive alternative when i. there does not exist a specialized differentially private alternative, or when ii. multiple processes applied in parallel can use the same pre-randomized input. A simple way to do input randomization is to compute perturbed histograms, which essentially are noisy multiset membership functions. Unfortunately, computation of perturbed histograms is only efficient when the data stems from a low-dimensional discrete space. The restriction to discrete spaces can be mitigated by discretization; Lei presented in 2011 an analysis of discretization in the context of M-estimators. Here we address the restriction regarding the dimensionality of the data. In particular we present a differentially private approximation algorithm for selecting features that preserve conditional frequency densities, and use this to project data prior to computing differentially private histograms. The resulting projected histograms can be used as machine learning input and include the necessary randomness for differential privacy. We empirically validate the use of differentially private projected histograms for learning binary and multinomial logistic regression models using four real world data sets.