title: Differences in smoking habits of MZ and DZ twins: a commentary on Tishler and Carey.
abstract: Tishler and Carey (this issue, 2007) have analyzed the difference in ever smoking prevalence between monozygotic (MZ) and dizygotic (DZ) twins in 8 published twin studies. They conclude that the lower prevalence in MZ twins might invalidate conclusions from classic twin models. I critique the conducted meta-analysis and suggest additional analyses to be conducted. A reanalysis of the Finnish Twin Cohort 1975 questionnaire data (included in Tisher and Carey) indicates that when intrapair correlations are correctly taken into account, the MZ-DZ difference in that study is no longer statistically significant. Even if the Tisher/Carey finding holds up in further analyses, it pertains only to the observed trait, the effect is small in size, and the mechanism underlying it needs to be explored.
authors: Department of Public Health, University of Helsinki, Helsinki, Finland. jaakko.kaprio@helsinki.fi
authors: Jaakko
authors: J
authors: Kaprio
mesh_terms: D006184:Habits; D006801:Humans; D008297:Male; D012907:Smoking / Q000235:genetics*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic