The Relationship Between Suggestibility and Intelligence in Delinquents
s John A. McGeoch Assistant Professor of Psychology, Washington University Two tests of suggestibility?the size-weight illusion and the progressive weights1?were given to thirty-five of the delinquents brought to the St. Louis Psychiatric Clinic2 for examination during January and February, 1924. The Stanford Revision of the BinetSimon Intelligence Scale was given to each as part of the routine work of the clinic. The suggestibility tests were given at the same sitting as the intelligence test, and according to the standard directions cited by Whipple3. The size-weight illusion was scored in terms of the difference in weight, in grams, between the two comparison blocks which the subjects selected as being equal in weight to the two standard blocks. The progressive weights were scored in terms of the number of times the judgment “heavier” was given in the last ten judgments. The I.Q.’s of the group range from 37 to 106, the average being 72.7, P.E. 18.2.
The correlations between the suggestibility scores and those made on the Stanford Revision are of some significance, and afford interesting data on a problem about which too little is known. In some cases high suggestibility seems to be one of the factors underlying delinquency, and it is worth while to know how suggestibility relates with intelligence. The coefficients of correlation (Pearson’s product-moment formula) are given below.
I. Q. with size-weight illusion r. = -.150 ? .110 I. Q. with progressive weights r. = -.472 ? .087 M. A. with size-weight illusion r. = -.118 ? .111 M. A. with progressive weights r. = -.421 ? .098 Size-weight illusion with progressive weights r. = -.005 ? .113 From these coefficients of correlation it appears that the relationship between the I.Q. and the size-weight illusion scores is small and inverse, with a P.E. which indicates that it is negligible. The relationship between I.Q. and progressive weight scores, however, is inverse and moderately high. When mental ages, instead of I.Q., is used, the same general relationship obtains between them 1 The weights used were, in both cases, the standard ones furnished by C. H. Stoelting Co. 2 Under the direction of Dr William Nelson. 3 Whipple, G. M. Manual of Mental and Physical Tests, Baltimore, Warwick and York, 1921, Vol. 2. 134 THE PSYCHOLOGICAL CLINIC as between suggestibility and I.Q. The correlation between the two suggestibility tests themselves is practically zero, which bears out Scott’s conclusion that there is no general suggestibility.4 If, in the case of the progressive weights, the times that the judgment “heavier” is given and the times that the judgment “lighter” is given are added together and correlated with I.Q. and size-weight illusion, the following results appear: I. Q. with progressive weights, H plus L r. = -.486 ? .086 Size-weight illusion with progressive weights H plus L r. = -.048 ? .113 The correlations here are only slightly higher than when the “heavier” judgments are used alone.
Inspection of the scatter-diagram shows that, for both suggestibility tests, the relationship between I.Q. and suggestibility is greater at the ends of the I.Q. distribution. The force of this can also be seen, if the suggestibility scores of those cases falling in the upper and lower ten per cent of I.Q.’s are considered. The figures are as follows: Lowest 10 per cent in I. Q. Size-weight average 51.00 Progressive wt. aver 10.00 Highest 10 per cent in I. Q. Size-weight average 32.00 Progressive wt. aver 2.70 The cases involved were unequally divided as to sex, there being twenty-six boys and nine girls, but, as they stand, the girls appear distinctly more suggestible than the boys. The averages of the I.Q.’s for the two sexes differ by only two points. The following table expresses the sex differences. Cases Size-weight illusion Progressive weights Boys 26 38.4 5.1 Girls 9 40.0 8.1
Summary
In the group studied, the relationship between suggestibility and intelligence is inverse. It is moderately high and inverse in the case of the progressive weights and slight in the case of the sizeweight illusion, the inverse relationship being greater in both instances at the ends of the intelligence distribution. The girls appear more suggestible than the boys, the difference being greater with the progressive weights. 4 Scott, W. D. Personal Differences in Suggestibility, Psychol. Rev. 1910, 17:147-154.
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