Privacy Risk Assessment: From Art to Science, By Metrics

Privacy risk assessments aim to analyze and quantify the privacy risks associated with new systems. As such, they are critically important in ensuring that adequate privacy protections for individual users are built in. However, current methods to quantify privacy risk rely heavily on experienced analysts who pick the "correct" risk level on a five-point scale. In this paper, we argue that a more scientific quantification of privacy risk increases accuracy and reliability and can thus make it easier to build privacy-friendly systems. We discuss how the impact and likelihood of privacy violations can be quantified and stress the importance of meaningful units of measurement. Finally, we argue that privacy risk metrics should be expressed as distributions instead of average values.