title: Concordance odds ratios and approximate rate ratios in longitudinal twin studies.
abstract: Odds ratios derived from probandwise concordance rates are usually interpreted as increased risks in twins. Though the odds ratios in case-control studies have been shown to reflect rate ratios, few studies focused on such relationships in twin studies. The authors derived an approximate formula for the ratios of person-time incidence rates after the random assignment of twins into index twins and co-twins, i.e., incidence rate ratios. The resulting rate ratio was estimated as the product of the concordance odds ratio and a term that reflect the follow-up duration and the average time to occurrence of disease. Odds ratios coincide with rate ratios when the average time to occurrence of disease is half the duration of follow-up, although in studies spanning several decades these two measures might be different. The authors illustrated that when the incidence rate is not constant over the follow-up period as in longitudinal twin studies, the conventional odds ratio should not be used as an estimator of rate ratio.
authors: Department of Preventive Medicine, University of Ulsan Seoul, Korea. leems@amc.seoul.kr
authors: Moo-Song
authors: MS
authors: Lee
authors: Sang-Il
authors: SI
authors: Lee
authors: Seungcheol
authors: S
authors: Yun
authors: Weechang
authors: W
authors: Kang
mesh_terms: D016022:Case-Control Studies; D003627:Data Interpretation, Statistical; D004812:Epidemiologic Methods; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D015233:Models, Statistical; D016017:Odds Ratio; D012680:Sensitivity and Specificity; D018433:Twin Studies as Topic / Q000379:methods* / Q000706:statistics & numerical data