the EPIC (European Prospective Investigation into Cancer and Nutrition) cohort (http://epic.iarc.fr). Collaborations involving diverse sample collections are therefore essential and efforts in this field are promising, for example the establishment of the Biobanking and BioMolecular Resource Infrastructure (www.bbmri.eu). With cohorts from different countries or even from different sites within the same country being used for genetic epidemiological research, the problem of confounding by population stratification has to be addressed. Fortunately, with the vast amount of the genome-wide data available, the actual extent and relevance of population genetic differences can be clarified with high confidence for most commonly used SNP sets.
