that this is a study of alcohol and nicotine dependency versus non-dependency. As such, we did not use a group of hypercontrols, but rather allowed AD and ND controls to represent the general population. This is similar to many other GWA studies in which controls are not explicitly sampled from the low tail of the risk distribution. For example, most controls in studies of cardiovascular disease are presumably carrying some atheromatous plaques but haven’t (yet) had the cardiovascular event which leads to the case diagnosis.
