Some problems in the study of differences in cognitive processes

To test whether groups differ in a particular ability, researchers often compare their performance on two tasks: an experimental task that is sensitive to the ability of interest and a control task that measures other influences on the experimental task. A group difference will be reflected in a differential deficit, a greater difference between groups in experimental task performance than in control task performance. Before concluding from such a result that the groups differ in the ability of interest, three methodological problems must be faced. First, a differential deficit may be an artifact of task differences in discriminating power. That is, the experimental task may be more sensitive than the control task to group differences in abilities other than the one of interest. Second, a differential deficit may be an artifact of group differences in familiarity with the stimuli or the task. Third, a group difference in one ability may be due to a difference in some other ability that is more, or less, general than the first. These problems affect research in a number of areas, including cognitive development, psychopathology, learning disabilities, and the theory of intelligence. We discuss some possible solutions to these problems.