On the use of mental tests for the measurement of disability after head injury, with a comparison between the results of these tests in patients after head injury and psychoneurotics.

WHERE knowledge of a medical condition is incomplete, there is a danger that the results of ancillary aids, especially when expressed in numerical terms, may acquire an unwarranted appearance of infallibility. The post-concussional state provides a good example of this tendency, for, while the core of the problem remains obscure, the results of investigations which have only presumptive relationships with the essential condition are liable to be accepted as direct, quantitative indicators of the total disablement. Radiology, psychometry, and electro-encephalography are all open to criticism on this score. For example, though the significance of sktul fracture is still uncertain, x-ray examination is commonly regarded as essential after head injury. It is perhaps fortunate that only the initiated can interpret an electro-encephalogram tracing; but the result of a psychometric test, usually expressed as a percentage deficit, is apt to stand out, in a case record, as the one fact on which the patient's condition can be assessed. There is no doubt that changes in personality occur after head injury in some cases, and, with them, what appear to be defects of intellectual function, usually at the higher levels. But it is almost certainly incorrect to suppose that intelligence tests measure only high-level intellectual activity; in fact they take a cross sectional sample of conscious mentation, in which affective elements play a most important part. Even in normal persons it is necessary to take account of such factors when a test score is interpreted; their presence in pathological cerebral states introduces, in the opinion of some writers, " an infinite source of error " (Goldstein, 1942a). Nevertheless, mental tests are widely used to measure quantitative intellectual impairment after head injury, and it was to investigate the usefulness of this method of examination that the experiment on which this paper is based was planned.