The post myocardial infarction exercise test: still worthy after all of these years.

preferable. In such a study design, an affected individual and other members of the family (parents if available, otherwise siblings) are ascertained and the probability of transmission of the different alleles at the locus under study from parents to the affected individual calculated. Because transmission is being studied, there is no problem with population substructure between cases and controls, although extreme care still needs to be paid to the technical issues of genotyping. We would suggest that any positive association discovered in a case-control study, however strongly supported by meta-analyses and appropriately sized studies, be regarded as preliminary until family studies confirm that the association is due to identity or proximity of the genotyped polymorphism to a causative genetic variant on the chromosome. Until such time, it seems prudent to adhere to the epidemiological principles of large size in individual studies and inclusivity in meta-analysis. B. KEAVNEY H. WATKINS Department of Cardiovascular Medicine, University of Oxford, Oxford, U.K. References