Reflections on PRAM

Peter-Paul de Wolf
José M. Gouweleeuw
Peter Kooiman
Leon Willenborg
Statistics Netherlands

Summary.
PRAM is a probabilistic, perturbative method for disclosure protection of categorical variables in microdata files. If PRAM is to be applied, several issues should be carefully considered. The microdata file will usually contain a specific structure, e.g., a hierarchical structure when all members of a household are present in the data file. To what extent should PRAM conserve that structure? How should a user of the perturbed le deal with variables that can (logically) be deduced from other variables on which PRAM has been applied? How should the probability mechanism, used to implement PRAM be chosen in the rst place? How well does PRAM limit the risk of disclosing sensitive information? In this paper, these questions will be considered.

Keywords:
Post RAndomisation Method (PRAM), disclosure limitation, perturbed data, Markov matrix, expectation ratio.

Address for correspondence:
Peter-Paul de Wolf
Statistics Netherlands
P.O. Box 4000
2270 JM Voorburg
The Netherlands
Phone: +31-70-3375060