Hagen, K., Zwart, J., Aamodt, A. H., Nilsen, K. B., Bråthen, G., Helde, G., . . . Stovner, L. J. (2009). The validity of questionnaire-based diagnoses: The third Nord-Trøndelag Health Study 2006–2008. Springer Milan.

Hagen, Knut, John-Anker Zwart, Anne Hege Aamodt, Kristian Bernhard Nilsen, Geir Bråthen, Grethe Helde, Marit Stjern, Erling A. Tronvik, và Lars Jacob Stovner. The Validity of Questionnaire-based Diagnoses: The Third Nord-Trøndelag Health Study 2006–2008. Springer Milan, 2009.

Hagen, Knut, et al. The Validity of Questionnaire-based Diagnoses: The Third Nord-Trøndelag Health Study 2006–2008. Springer Milan, 2009.