Limitations in our analyses include those related to phenotype, linkage and association analyses. The original smoking withdrawal data was collected using a paper-based questionnaire to catalogue respondents’ withdrawal symptoms; respondents may have had trouble recalling their symptoms, and therefore these data may suffer from recall bias. Responses to nicotine withdrawal symptoms were characterized using a 0 to 3 Likert scale and therefore measurement error may exist. It is possible that false positive linkage or association results arose in these analyses, though we assessed the empirical significance of linkage and the likelihood of false positive associations to facilitate the interpretation of significance.
