Stefansson is probably best known for the contribution he and his deCODE colleagues have made to the discovery of genetic variations linked to risk of disease and to a range of other traits. The population approach — the scale and breadth of resources and the focus on cross-mining disparate datasets — has been key to this productivity. It makes it possible to use both broad and rigorous definitions of phenotypes, rapidly test ideas, and for deCODE scientists to follow where the data leads rather than their own hypotheses.  This has led to a range of discoveries that link diseases and at times use the genetics even to redefine phenotypes in unusual ways, and Stefansson has spent significant time explaining these discoveries and their utility to the scientific and lay media. Typically, discoveries made in Iceland are published alongside validation in outside populations. Conversely, deCODE has often used its resources to validate discoveries made elsewhere. Among the more noteworthy of these discoveries are, by disease and trait: