Karl O. Christiansen (1. januar 1968), "Threshold of tolerance in various population groups illustrated by results from Danish criminological twin study, Threshold of Tolerance in Various Population Groups Illustrated by Results from Danish Criminological Twin Study", International psychiatry clinics, 5 (3): 107-120, doi:10.1002/9780470719640.CH8, PMID4886267, Wikidata Q39327636
Karl O. Christiansen (1. januar 1968), "Threshold of tolerance in various population groups illustrated by results from Danish criminological twin study, Threshold of Tolerance in Various Population Groups Illustrated by Results from Danish Criminological Twin Study", International psychiatry clinics, 5 (3): 107-120, doi:10.1002/9780470719640.CH8, PMID4886267, Wikidata Q39327636
Karl O. Christiansen (1974), "Seriousness of criminality and concordance among Danish twins", Crime, criminology and public policy: Essays in honour of Sir Leon Radzinwoiez, Wikidata Q98070993
Karl O. Christiansen (1. januar 1968), "Threshold of tolerance in various population groups illustrated by results from Danish criminological twin study, Threshold of Tolerance in Various Population Groups Illustrated by Results from Danish Criminological Twin Study", International psychiatry clinics, 5 (3): 107-120, doi:10.1002/9780470719640.CH8, PMID4886267, Wikidata Q39327636