Written by Christopher Riederer, Vijay Erramilli, Mauro Cherubini, Rodrigo de Oliveira and myself, this paper is the conclusion of a user study we conducted by the end of 2011 in Telefónica I+D. It has been accepted for publication in the proceedings of the 22nd International World Wide Web Conference (WWW2013). The abstract:

Most online service providers offer free services to users and in part,these services collect and monetize personally identifiable information (PII),primarily via targeted advertisements. Against this backdrop of economic exploitation of PII, it is vital to understand the value that users put to their own PII.Although studies have tried to discover how users value their privacy,little is known about how users value their PII while browsing,or the exploitation of their PII. Extracting valuations of PII from users is non-trivial – surveyscannot be relied on as they do not gatherinformation of the context where PII is being released,thus reducing validity of answers. In this work, we rely on refined Experience Sampling – a data collection method that probes users to valuate their PII at the time and place where it wasgenerated in order to minimize retrospective recall and henceincrease measurement validity. For obtaining an honest valuation of PII, we use a reverse second price auction. We developed a web browser plugin and had 168 users – living in Spain -install and use this plugin for 2 weeksin order to extract valuations of PII in different contexts.
We found that users value items of their online browsing historyfor about 7€ (10USD), and they give higher valuations to their offline PII, such as age and address (about 25€ or 36USD).When it comes to PII shared in specific online services, users value informationpertaining to financial transactions and social network interactionsmore than activities like search and shopping. No significantdistinction was found between valuations of different quantities of PII (e.g. one vs. 10 search keywords), but deviation was foundbetween types of PII (e.g. photos vs. keywords). Finally, the users’ preferred goods for exchanging their PII included money and improvements in service, followed by getting more free services and targeted advertisements.