From privacy methods to a privacy toolbox: Evaluation shows that heuristics are complementary

We describe the two-year-long development and evaluation of the Proportionality Method, a design method intended to aid HCI practitioners in designing advanced IT applications with complex privacy implications. The method is inspired by Data Protection Authorities' (DPA) and Courts' practice and proposes to balance the impact on privacy of IT applications with their usefulness. We discuss the results of an evaluation of the design method to verify its usability, usefulness and effectiveness vis-à-vis other design methods proposed in the HCI literature to address similar issues. Results suggest that different design methods for privacy highlight different sets of issues and a combination of methods should be employed in a comprehensive design process. We propose to judge design methods based on their overall quantitative and qualitative merits, including the type of application and technology for which they are most fit and their methodological approach. We finally propose to develop a privacy toolbox, that is, a set of heuristic methods that designers can choose from with knowledge and understanding of their relative advantages and limitations.