Epistemic Parity: Reproducibility as an Evaluation Metric for Differential Privacy
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Differential privacy mechanisms are increasingly used to enable public release of sensitive datasets, relying on strong theoretical guarantees for privacy coupled with empirical evidence of utility. Utility is typically measured as the error on representative proxy tasks, such as descriptive statistics, multivariate correlations, or classification accuracy. In this paper, we propose an alternative evaluation methodology for measuring the utility of differentially private synthetic data in scientific research, a measure we term "epistemic parity." Our methodology consists of reproducing empirical conclusions of peer-reviewed papers that use publicly available datasets, and comparing these conclusions to those based on differentially private versions of the datasets. We instantiate our methodology over a benchmark of recent peer-reviewed papers that analyze public datasets in the ICPSR social science repository. We reproduce visualizations (qualitative results) and statistical measures (quantitative results) from each paper. We then generate differentially private synthetic datasets using state-of-the-art mechanisms and assess whether the conclusions stated in the paper hold. We find that, across reasonable epsilon values, epistemic parity only partially holds for each synthesizer we evaluated. Therefore, we advocate for both improving existing synthesizers and creating new data release mechanisms that offer strong guarantees for epistemic parity while achieving risk-aware, best effort protection from privacy attacks.
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