Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Selection bias is a statistical bias in which there is an error in choosing the individuals or groups to take part in a scientific study. It is sometimes referred to as the selection effect. The term "selection bias" most often refers to the distortion of a statistical analysis, resulting from the method of collecting samples. If the selection bias is not taken into account then any conclusions drawn may be wrong.