Øyeflaten, I., S. A. Lie, C. Ihlebæk, S. Brage, and H. R. Eriksen. “Comparison of Self-Reported and Register Data on Sickness Absence Among Norwegian Patients Participating in an Occupational Rehabilitation Program”. Norsk Epidemiologi, vol. 19, no. 2, Jan. 2010, doi:10.5324/nje.v19i2.586.