TASK-DIFFICULTY AND COGNITIVE DEFICITS IN SCHIZOPHRENIA

Investigators of schizophrenic cognition often produce 2 or more tasks of differing difficulty levels by manipulating a variable that affect s the accuracy of both normal and schizophrenic individuals; the inves tigators find that the variable also affects the difference between th e groups in accuracy and conclude that the variable taps a schizophren ic differential deficit. An alternative hypothesis is that task differ ences in true-score variance artifactually produce the finding. For fr ee-response tasks, group differences tend to be larger when difficulty is near 50%. The authors illustrate a new method of controlling this artifact by selecting items for hard and easy tasks on opposite sides of 50% difficulty and equidistant from it. Using this design with an a nagram task, they found that schizophrenic and normal individuals diff er no more on hard anagrams than on easy ones, and they propose the de sign for testing hypotheses concerning schizophrenic deficit on tasks that differ in difficulty.