considered to be genetically homogeneous. As such, the use of better selected controls and examination of ancestry informative markers may address these issues to an extent. The use of intermediate phenotypes, as discussed below, may also help improve reproducibility of studies by reducing the heterogeneity between studies. Publication bias, where positive results are more likely to be published, may inflate the apparent effect of a genetic variant and its association to addiction outcomes. Care must also be taken to ensure that claims of replication of data are made with sound justification to avoid further confusion in the literature. These issues occur widely in genetic research, including studies in drug addiction, and need to be considered in the design of future genetic studies.
