Preserving temporal relations in clinical data while maintaining privacy

Abstract

Objective: Maintaining patient privacy is a challenge in large-scale observational research. To assist in reducing the risk of identifying study subjects through publicly available data, we introduce a method for obscuring date information for clinical events and patient characteristics.

Methods: The method, which we call Shift and Truncate (SANT), obscures date information to any desired granularity. Shift and Truncate first assigns each patient a random shift value, such that all dates in that patient's record are shifted by that amount. Data are then truncated from the beginning and end of the data set.

Results: The data set can be proven to not disclose temporal information finer than the chosen granularity. Unlike previous strategies such as a simple shift, it remains robust to frequent - even daily - updates and robust to inferring dates at the beginning and end of date-shifted data sets. Time-of-day may be retained or obscured, depending on the goal and anticipated knowledge of the data recipient.

Conclusions: The method can be useful as a scientific approach for reducing re-identification risk under the Privacy Rule of the Health Insurance Portability and Accountability Act and may contribute to qualification for the Safe Harbor implementation.

Figure 1:

Shift and Truncate. Each row is a unique patient, each number is a unique data point for a patient, and each rectangle represents the time that the patient was potentially observed. ( a ) Original data set. Patients are potentially observed for 3 years (each vertical line marks 1 year). Patients need not have data, but simply the potential to have been observed (even if they lived elsewhere or were not born yet, someone had the potential to have been observed). ( b ) Shifted data set. Patient records are shifted forward by 1–366 days. Data points that were previously aligned across patients are no longer aligned, but points within a given patient remain at the same relative distances from each other. ( c ) Shifted and truncated data set. Data points from the first 366 days of the shifted data set and from the last 366 days of the shifted data set are removed from the data set.