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The Abilities of Adolescent and Adult High-Grade Male Defectives

Medical Research Council, Occupational Psychiatry Research Unit, Maudsley Hospital, Denmark Hill, London, S.E.5

N. O'Connor, M.A. and J. M. Crawford, M.D., D.P.M.

ABSTRACT

1. Literature bearing on the intelligence of mentally defective adults is reviewed. It is concluded that psychiatric practice still accepts a Binet I.Q. of between 70 and 75 as marking the upper limit of mentally defective intelligence, despite the fact that the versions of the test upon which these standards were originally based are no longer in use. The 1937 Stanford Revision of the Binet test, which has replaced them, has greater standard deviations, so that about ten times as many adults would have I.Q.'s as low as 70 on this as had I.Q.'s of 70 on older versions of the test. The use of the Binet test as an adult intelligence test is criticized, and it is pointed out that no test at present in use can be considered satisfactory; the Wechsler Bellevue test, which is the best individual adult intelligence test available, has been standardized for an American, but not an English population.
   The concept of "the" intelligence quotient is criticized, and difficulties in the way of deciding whether defectives are relatively more retarded in some respects (e.g. verbal intelligence) than in others (e.g. practical ability) are discussed.
   
2. The inadequacies of our present knowledge regarding cognitive abilities of defectives which are believed to be not highly correlated with intelligence are pointed out.
   
3. Results of a battery of 18 cognitive tests given to a sample of 104 high-grade adolescent and adult male defectives, resident in an M.D. institution, are presented and discussed. The following results were found:
   1. The mean and median I.Q.'s in five intelligence tests were, when corrected for differences in standard deviation, all over 70 points.
      
   2. The correlations between the tests were positive and significant, except for those between the Binet Vocabulary and other tests, which were not significant.
      
   3. Our research gave I.Q.'s which were in many cases considerably higher than one would have expected to find from reading reports made by certifying officers about the cognitive abilities of the patients. (No evidence for this statement was presented.).
      
   4. The test scores on the United States Employment Service General Aptitude Test Battery which was given to the patients showed them to be less retarded in Form Perception and Spatial Aptitude than in Hand-eye co-ordination, Manual Dexterity, Finger Dexterity, and Motor Speed.
      
   
   
4. Difficulties in the interpretation of these results are discussed. The use of the General Aptitude Test Battery for vocational guidance purposes is questioned.
   
5. There are probably more dull or subnormal (rather than cognitively defective) adults in M.D. institutions than appears to be generally realized to-day.
   
6. The separation of high-grade from low-grade cases, by placing them in institutions designed to deal explicitly with just this type of patient, is urged.
   

Received for publication July 1, 1950.