The rise and fall of an opt-out system.

In Denmark, citizens participate in register-based research without the possibility of opting out. However, in 1995 it was made possible for Danish citizens to register an opt-out called 'researcher protection' [], which implied that researchers could not contact people to invite them to participate in research projects, such as clinical trials or questionnaries, based on their registrations in national registers. Data already registered could still be used for research. In 2014, this possibility of opt-out was revoked by law. The aims of this paper are to understand how the Danish researcher protection system came about, why it was terminated and what we can we learn from this example. We conducted a descriptive analysis of a copy of the former researcher protection register along with policies and media debate surrounding the rise and revocation of the researcher protection system. Our results show how both the inception and the abolishment of researcher protection appear to be ad hoc and without specified criteria of success. An examination of the recorded entries in the researcher protection registry could have led to changes in its administration as an alternative to its total abolition.