More than 20 genomewide linkage scans on smoking behavior have been performed using a variety of smoking behavior assessments, including DSM-IV defined nicotine dependence, the Fagerstrom Test for Nicotine Dependence (FTND) (3, 4), the Fagerstrom Tolerance Questionnaire (FTQ), Fagerstrom-derived smoking quantity (SQ) and Heaviness of Smoking Index (HSI), habitual smoking, persistent smoking, maximum number of cigarettes smoked in a 24-hour period (MaxCigs24), and others (5–24). Numerous putative susceptibility loci have been identified, but only a few of these have been replicated in independent studies, which is not uncommon for linkage analysis of genetically complex traits. Considering the high likelihood of many risk loci of low-to-moderate effect for complex traits and the relatively small sample size in each study, the discrepancy among study results is expected, because a single study may be statistically underpowered to detect a low magnitude but real genetic linkage. Although literature reviews have provided valuable overviews of progress in linkage studies on smoking behavior, they are not intended to provide formal statistical assessment of pooled evidence for linkage across studies. Considering the quantity of accumulated genome scan
