A new tool for applying controlled rounding to a statistical table in Microsoft Excel

Abstract

Rounding Methods are perturbation techniques used by statistical agencies for protecting privacy when publishing aggregated data like frequency tables. Controlled rounding is one of these methods that, besides the possibility of publishing clearer rounded tables that still respect the additivity underlying the original table, also offers an effective and powerful way to protect the unsafe data. Due to the lack of automatic procedure, it is at present still not used much, and statistical agencies apply less sophisticated variants (e.g., random rounding) which have several disadvantages. This work presents an automatic procedure to apply Controlled Rounding in a simple and friendly way on a personal computer. The tool is written in C programming language, using Excel SDK-API, and is implemented as an add-in for Microsoft Excel - a standard software we chose due to its wide spread on many personal computers and because of its familiarity to many users who work with tabular material in statistical agencies. The algorithm is based on solving an integer linear program in order to find a "good" rounded table while ensuring additivity and protection, as recently proposed by the first author. An extra feature of the here-presented implementation is that it does not need to be linked with a commercial mathematical programming software; better performance on large scale tables would be obtained when Xpress or Cplex is available on the computer. © Springer-Verlag 2004.