From the disease-mapping point of view, population stratification is important in the analysis of association genetic data, especially when that **data** is being used to infer the contribution of genetics to a disease. The presence of undetected population structure can mimic association (leading to more false positives) or mimic lack of association (leading to false negatives) [19]. While there Unrooted radial neighbour-joining tree showing the genetic relationships of the four populations groups studied Figure 3 Unrooted radial neighbour-joining tree showing the genetic relationships of the four populations groups studied.