title: Comparing correlations of continuous observations from two independent populations using a sequential approach.
abstract: A sequential study design generally makes more efficient use of available information than a fixed sample counterpart of equal power. This feature is gradually being exploited by researchers in genetic and epidemiological investigations that utilize banked biological resources and in studies where time, cost and ethics are prominent considerations. Recent work in this area has focussed on the sequential analysis of matched case-control studies with a dichotomous trait. In this paper, we extend the sequential approach to a comparison of the associations within two independent groups of paired continuous observations. Such a comparison is particularly relevant in familial studies of phenotypic correlation using twins. We develop a sequential twin method based on the intraclass correlation and show that use of sequential methodology can lead to a substantial reduction in the number of observations without compromising the study error rates. Additionally, our approach permits straightforward allowance for other explanatory factors in the analysis. We illustrate our method in a sequential heritability study of dysplasia that allows for the effect of body mass index and compares monozygotes with pairs of singleton sisters.
authors.affiliation: Medical Research Council Epidemiology Unit, Strangeways Research Laboratory, Worts Causeway, Cambridge CB1 8RN, UK. fb284@medschl.cam.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: Fazil Baksh
authors.forename: Gerco
authors.initials: G
authors.lastname: Haars
authors.forename: Susan
authors.initials: S
authors.lastname: Todd
authors.forename: Paulus A H
authors.initials: PA
authors.lastname: Van Noord
authors.forename: John
authors.initials: J
authors.lastname: Whitehead
mesh_terms: D003627:Data Interpretation, Statistical; D004812:Epidemiologic Methods; D005260:Female; D005348:Fibrocystic Breast Disease / Q000235:genetics; D006801:Humans; D018401:Sample Size; D018433:Twin Studies as Topic; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics