a comparison of values obtained by different experimental groups on an outcome or dependent variable when two or more predictor or independent variables vary simultaneously across the groups. In such cases it is impossible to differentiate the effects of the independent variables. For example, consider a researcher studying how material presentation format (lecture vs. computer) and teacher sex (male vs. female) affect student learning. If the investigator were to examine data for only two groups of students (those who had a male teacher and lecture presentation format vs. those who had a female teacher and computer presentation format), he or she would have created a confounded comparison.