1. Hauge M, Harvald B, Fischer M, et al. The Danish Twin Register. Acta Genet Med Gemellol. 1968;17:315–31.
2. Cederlöf R. The twin method in epidemiologic studies on chronic disease. Diss Acad. University of Stockholm, 1966.
3. Magnus P, Berg K, Nance WE. Predicting zygosity in Norwegian twin pairs born 1915–1960. Clin Genet. 1983;24:103–12.
4. Kaprio J, Koskenvuo M, Sarna S. Cigarette smoking, use of alcohol, and leisure-time physical activity among same-sexed adult male twins. In: Gedda L, Parisi P, Nance WE, eds. Twin research 3: part C, Epidemiological and clinical studies. New York: Alan R. Liss, Inc; 1981:37–46.
5. Jablon S, Neel JV, Gersowitzh H, et al. The NAS-MRC Twin Panel: Methods of construction of the panel, zygosity diagnoses, and proposed use. Am J Hum Genet. 1967;19:133–61.