title: Relationship between case-control studies and the transmission/disequilibrium test.
abstract: Case-control studies provide a powerful approach for detecting disease susceptibility loci that have only a weak to moderate impact on the risk of disease, or markers that are in linkage disequilibrium with such loci. However, since any association detected in a case-control study may result from uncontrolled confounding, evidence for disease-marker associations obtained from such studies must be confirmed by alternative methods. Since studies that use the transmission/disequilibrium test or TDT are frequently employed to confirm disease-marker associations detected in case-control studies, data are increasingly available from both case-control studies and "TDT studies" of the same disease-marker association. It would, therefore, be useful to have a single measure of the magnitude of the disease-marker association that would allow for comparison of results from these two study designs. Such a measure could also be used to estimate minimum sample size requirements for TDT studies of previously reported disease-marker associations. An obvious measure of the disease-marker association in TDT studies is the frequency (T) with which heterozygous parents transmit the putative, high-risk marker allele to affected offspring. In this paper, it is shown that T can also be estimated from case-control data with a minimum of assumptions, and that T is the critical parameter for determining power and estimating sample sizes for the TDT.
authors.affiliation: Department of Biostatistics and Epidemiology, The University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. lauramit@mail.med.upenn.edu
authors.forename: L E
authors.initials: LE
authors.lastname: Mitchell
mesh_terms: D016022:Case-Control Studies; D015986:Confounding Factors, Epidemiologic; D003627:Data Interpretation, Statistical; D015340:Epidemiologic Research Design; D005787:Gene Frequency / Q000235:genetics*; D005819:Genetic Markers / Q000235:genetics*; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D005838:Genotype; D006579:Heterozygote; D006801:Humans; D015810:Linkage Disequilibrium / Q000235:genetics*; D012307:Risk Factors; D018401:Sample Size
chemical_list: D005819:Genetic Markers