Post Randomisation for Statistical Disclosure Control: Theory and Implementation

J.M. Gouweleeuw, P. Kooiman, L.C.R.J. Willenborg, and P.-P. de Wolf

Abstract:
The Post RAndomisation Method (PRAM) is a perturbative method for disclosure protection of categorical variables. Applying PRAM means that for each record in a microdata file the score on a number of variables is changed according to a specified probability mechanism. This article considers the effect of PRAM on both the safety of the data and the statistical quality of the data. When applying PRAM in practice, a number of decisions have to be made, as for example to which variables and in what way to apply PRAM. These issues are briefly discussed in this article. As an example, the result of an investigation performed at Statistics Netherlands into the possibility of protecting the Dutch National Travel Survey using PRAM is presented.

Keywords:
Post RAndomisation Method (PRAM); disclosure; perturbed data; randomised response; Markov matrix; invariant matrix; noise; Dutch National Travel Survey.