Epidemiological methods for studying genes and environmental factors in complex diseases

Exploration of the human genome presents new challenges and opportunities f or epidemiological research. Although the case-control design is quicker an d cheaper for study of associations between genotype and risk of disease th an the cohort design, cohort studies have been recommended because they can be used to study gene-environment interactions. Although the scientific re levance of statistical Interaction Is pertinent, the main disadvantage of t he case-control design-susceptibility to bias when estimating effects of ex posures that are measured retrospectively-does not necessarily apply when s tudying statistical interaction between genotype and environmental exposure . Because correctly designed genetic association studies are equivalent to randomised comparisons between genotypes, conclusions about cause can be dr awn from genetic associations even when the risk ratio is modest. For adequ ate statistical power to detect such modest risk ratios, the case-control d esign is more feasible than the cohort design.