To conduct more detailed analyses, the researchers subsequently selected a subset of families with at least three alcohol-dependent members as the stage II sample. For these families, the investigators also recruited more distant biological family members if a member from that branch of the family was alcohol dependent. For all stage II participants, researchers completed a more detailed evaluation and collected blood samples to obtain DNA for genetic studies. Thus, this stage II group of families that were severely affected with alcohol dependence was used for the genetic studies of alcohol dependence and habitual smoking discussed later in this article.
