title: A genetic and environmental analysis of obsessionality in normal twins.
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003192:Compulsive Behavior / Q000235:genetics*; D005260:Female; D005824:Genetics, Behavioral; D006801:Humans; D008297:Male; D008875:Middle Aged; D008957:Models, Genetic; D009770:Obsessive Behavior / Q000235:genetics*; D011247:Pregnancy; D012931:Social Environment; D013223:Statistics as Topic; D014427:Twins / Q000523:psychology*; D014429:Twins, Dizygotic / Q000523:psychology*; D014430:Twins, Monozygotic / Q000523:psychology*