LETTERS TO THE EDITOR
than it is at present. Debate Forum. 1. Am. Acad. Child Adolesc.
Psychiatry , 30:685-69 1.
Fetal Alcohol Syndrome To the Editor: With reference to fetal alcohol syndrome (FAS), Streissguth et a!. (199 1) noted , " From the standp oi nt of co mm unity planning and pa tien t management , it is extremely important to know the long-term consequences of this preve ntab le birth defect. Specifically, it must be know n how predictable later inte llect ual leve l is fro m ear lier IQ tests obtained at an age when suc h tests are most likely to be administered " (p. 584 ). Streiss guth et a!. therefore co nducte d a study of IQ stability in ind ividuals wit h FA S and with possibl e fetal alcohol effects (FA E). Given that FAS has now been identified as the leading known cau se of ment al retardation in the United States, the topic and intent of the Strei ssg uth et a!. inves tigation can only be co nside red of utmost importance. Streissguth et a!. concl uded that, " IQ scores of adolesce nts and adults with both FAS and FAE rem ained quite stable over time " (p. 585) or " actually . . . decl ine[d]" (p. 586). However, (I ) the di verse set of intelligence tests admin istered, and (2) the statistical treatm ent of the data derived therefrom suggest that the conclusion is unce rtain . A variety of intelli gence scale s were used to generate data for this s tudy. T est s incl ud ed th e St a nford-B in et , WIS C-R, WA IS, and WAIS-R . But these scales yield substantially different estimates of intelligence when used with ment ally retarded individ uals (e.g., Sp itz, 1988). O ne can ex pect, for example, a me an 8- or 9-point disparity bet ween the WISC and W ISC- R, as administered to ment ally retarded subj ects. By interpol ation, the same poin t could be made with regards to the Stanford-Bin et and the WI SC-R (Fi sher et a!., 1961). Similarly, a mea n 12-point discrepancy has been rep orted between WISC-R and WAIS-R Full-Sca le IQs and a 19-poi nt di fference bet ween StanfordBinet and WAIS-R. More over, the inter-scale discrepancies are not constant but dep end on the age (Fisher et a!., 196 1) and intellectual level (Spitz, 1988) of the examinee . In terms of the study under review, these data sugge st that mean IQs a nd me an IQ differences mu st be interprete d with e xtrem e caution-the potential scope of confounding is huge. Indeed, considerations such as these may wh olly explain the 20-point IQ increase obtai ned by one patient specifically mentioned in the article . Streissguth et al. dem onstrated IQ stability with three statistica l procedure s: I. Th ey showe d that mean IQ scores from Tes t I to Test 2 were very clo se (66 , 67 for FAS ; 80, 82 for FAE ). Th is informatio n is necessary for the evaluation of IQ stability, of course, but its shortcoming is that group me ans can remain stabl e, whereas individual data points fluctuate wildly. Thu s, Atki nson et a!. (in pre ss) found a mean 1.79-point difference betwee n two intelligen ce scales that co rrelated 0.78 , but indiv idual scores varied between - 12 and 22 poin ts, and, in 29% of the cases, the difference was statistically significant (i.e., exceeded I I to 14 points, dependin g on age ). 2. Streissguth et al. also dem onstrated high test-retest correlations (0.78 for FAS, 0.88 for FAE). As impressive as these correlations are, how ever, they lea ve 1.0 - 0.78 2 = 39% and 1.0 - 0.882 = 23% of the variance unexplained (FAS, FAE, respectively). Again, this lea ves room for IQ fluctuation at the level of individu al IQ sco res. 3. Perhaps, recognizing this difficulty, the author s attempted to measur e IQ cha nge at the level of the individual. Streissguth et al. are to be co mmen ded for this strategy; many, maybe most, in vestigators stop after assessing gro up differences and intercorrelations. Streissguth et al. used , as a criterio n o f intra -indivi dual IQ fluctuat ion, the standard deviation of the W ech sler scal es, 15. The y found that only seven of 40 patients (17.5%) showe d an IQ change of this magnitude
J. Am. Acad. Child Adolesc. Psychiatry, 31:3, May 1992
or grea ter. Howe ver, the authors' estimate of IQ stability may be exaggerated because this standard deviatio n is not appropriate for measuring change in the individual. The ap propriate statistic to measure intra-indi vidual variation is the standard error of prediction . This can be mult iplied by 1.96 to determine cha nge sig nific ant at the 0.05 level. To illu strate, the med ian standard error of prediction for the WAIS-R is 3.62 (Knight, 1983); 3.62 X 1.96 = 7. 1. Thi s is less than half the size of the standard de viation used by Stre issgu th et a!., suggesting that approxi mately 14 (35 %), not se ven (17 .5%), of the individu als in the sample obtained IQ change scores beyond the 0.05 significance level (although the subs tantive meaning of this estimate is clouded by the diversity of IQ scales utilized). It is possible, then , that a subs tantia l proport ion of individu als tested did not show IQ stabi lity acro ss time. In sum, Streissguth et al. attempted to answer an important question with ava ilable data. The study was worthwhile, giv en the con straints of their data base. Howev er, becau se of these co nstrai nts, and in view of some statistical limitations, the co nclusio ns regard ing IQ stability may need qualification . Leslie Atki nso n, Ph.D . Univers ity of To ront o, Onta rio REFERENCES
Atkinson, L., Bevc, I., Dickens, S. & Blackwell , J. (in pre ss), Concur rent vali dities of the Stan ford-Bin et (Fourth Editio n), Lei ter, and Vi neland wit h deve lopme ntally delayed children. Journal ofSchool
Psychology. Fisher, G. M., Kilman, B. A. & Shortwe ll, A. M. (196 1), Comparability of inte lligence quotients of ment al defecti ves on the Wec hsle r Adult Intelli gence Scal e and the revision of the Stanford-Binet. J. Consult. Clin. Psychol., 25 :192-195. Knight , R. G. ( 1983), On interpreting the seve ral standard errors of the WAIS-R : some further tables. J. Consult. Clin. Psychol., 5 1:67 1-673. Spi tz, H . H . ( 198 8), In ver s e relati on sh ip bet ween th e WISC -RI WA IS-R score disparity and IQ level in the lower rang e of intelligence . Am. J. Ment. Defi c., 92:376-3 78. Strei ssguth, A. P., Rand els, S. P. & Smith, D. F. ( 199 1), A testretest study of intellige nce in patient s with fetal alcohol syndrom e: implications for care. J. Am. Ac ad . Child Adolesc. Psy ch iatry, 30:584-587.
The authors reply: Our rece nt art icle in the Journal was an attempt to share data from our cli nica l files with other cl inicians who have had little opportunity to exami ne childre n with Fetal Alcoho l Syndrome (FAS) or to see them over an extended period of their lives. We have been co ncerned about the discrepancy between the small number of reports in the scientific literature on group s of children with FAS , especially in co mpar ison with the magn itude of the probl em . Contrast this with autism, for example, to which an entire journa l is devoted , or eve n with much more esoteric groups of children with well-k nown psychiatric diagnoses, such as Tour ette ' s syndro me. Clinical data are never as pure as that obtai ned solely for research purposes, as Dr. Atki nso n po ints out. However , it is what clinicia ns deal with on a day -to-day basis in making decisions about thei r patien ts and in trying to help families under stand the problems they face in providin g for d isabled child ren across the life- span. The data in our article are pro babl y at least as goo d as that ava ilable to most clin icians in estima ting children's intellectual fu nctio ning . It is true that Test 1 and Test 2 were ofte n perform ed with di fferent tests-that is because neither the W ISC- R or the WAIS -R spans the ages represented in this rep ort. Furthermo re, when deali ng with patient s of such varied age s acr oss the life-span, it is inevitable that different stand ardization form s of the individual IQ tests have been employed.
563
than it is at present. Debate Forum. 1. Am. Acad. Child Adolesc.
Psychiatry , 30:685-69 1.
Fetal Alcohol Syndrome To the Editor: With reference to fetal alcohol syndrome (FAS), Streissguth et a!. (199 1) noted , " From the standp oi nt of co mm unity planning and pa tien t management , it is extremely important to know the long-term consequences of this preve ntab le birth defect. Specifically, it must be know n how predictable later inte llect ual leve l is fro m ear lier IQ tests obtained at an age when suc h tests are most likely to be administered " (p. 584 ). Streiss guth et a!. therefore co nducte d a study of IQ stability in ind ividuals wit h FA S and with possibl e fetal alcohol effects (FA E). Given that FAS has now been identified as the leading known cau se of ment al retardation in the United States, the topic and intent of the Strei ssg uth et a!. inves tigation can only be co nside red of utmost importance. Streissguth et a!. concl uded that, " IQ scores of adolesce nts and adults with both FAS and FAE rem ained quite stable over time " (p. 585) or " actually . . . decl ine[d]" (p. 586). However, (I ) the di verse set of intelligence tests admin istered, and (2) the statistical treatm ent of the data derived therefrom suggest that the conclusion is unce rtain . A variety of intelli gence scale s were used to generate data for this s tudy. T est s incl ud ed th e St a nford-B in et , WIS C-R, WA IS, and WAIS-R . But these scales yield substantially different estimates of intelligence when used with ment ally retarded individ uals (e.g., Sp itz, 1988). O ne can ex pect, for example, a me an 8- or 9-point disparity bet ween the WISC and W ISC- R, as administered to ment ally retarded subj ects. By interpol ation, the same poin t could be made with regards to the Stanford-Bin et and the WI SC-R (Fi sher et a!., 1961). Similarly, a mea n 12-point discrepancy has been rep orted between WISC-R and WAIS-R Full-Sca le IQs and a 19-poi nt di fference bet ween StanfordBinet and WAIS-R. More over, the inter-scale discrepancies are not constant but dep end on the age (Fisher et a!., 196 1) and intellectual level (Spitz, 1988) of the examinee . In terms of the study under review, these data sugge st that mean IQs a nd me an IQ differences mu st be interprete d with e xtrem e caution-the potential scope of confounding is huge. Indeed, considerations such as these may wh olly explain the 20-point IQ increase obtai ned by one patient specifically mentioned in the article . Streissguth et al. dem onstrated IQ stability with three statistica l procedure s: I. Th ey showe d that mean IQ scores from Tes t I to Test 2 were very clo se (66 , 67 for FAS ; 80, 82 for FAE ). Th is informatio n is necessary for the evaluation of IQ stability, of course, but its shortcoming is that group me ans can remain stabl e, whereas individual data points fluctuate wildly. Thu s, Atki nson et a!. (in pre ss) found a mean 1.79-point difference betwee n two intelligen ce scales that co rrelated 0.78 , but indiv idual scores varied between - 12 and 22 poin ts, and, in 29% of the cases, the difference was statistically significant (i.e., exceeded I I to 14 points, dependin g on age ). 2. Streissguth et al. also dem onstrated high test-retest correlations (0.78 for FAS, 0.88 for FAE). As impressive as these correlations are, how ever, they lea ve 1.0 - 0.78 2 = 39% and 1.0 - 0.882 = 23% of the variance unexplained (FAS, FAE, respectively). Again, this lea ves room for IQ fluctuation at the level of individu al IQ sco res. 3. Perhaps, recognizing this difficulty, the author s attempted to measur e IQ cha nge at the level of the individual. Streissguth et al. are to be co mmen ded for this strategy; many, maybe most, in vestigators stop after assessing gro up differences and intercorrelations. Streissguth et al. used , as a criterio n o f intra -indivi dual IQ fluctuat ion, the standard deviation of the W ech sler scal es, 15. The y found that only seven of 40 patients (17.5%) showe d an IQ change of this magnitude
J. Am. Acad. Child Adolesc. Psychiatry, 31:3, May 1992
or grea ter. Howe ver, the authors' estimate of IQ stability may be exaggerated because this standard deviatio n is not appropriate for measuring change in the individual. The ap propriate statistic to measure intra-indi vidual variation is the standard error of prediction . This can be mult iplied by 1.96 to determine cha nge sig nific ant at the 0.05 level. To illu strate, the med ian standard error of prediction for the WAIS-R is 3.62 (Knight, 1983); 3.62 X 1.96 = 7. 1. Thi s is less than half the size of the standard de viation used by Stre issgu th et a!., suggesting that approxi mately 14 (35 %), not se ven (17 .5%), of the individu als in the sample obtained IQ change scores beyond the 0.05 significance level (although the subs tantive meaning of this estimate is clouded by the diversity of IQ scales utilized). It is possible, then , that a subs tantia l proport ion of individu als tested did not show IQ stabi lity acro ss time. In sum, Streissguth et al. attempted to answer an important question with ava ilable data. The study was worthwhile, giv en the con straints of their data base. Howev er, becau se of these co nstrai nts, and in view of some statistical limitations, the co nclusio ns regard ing IQ stability may need qualification . Leslie Atki nso n, Ph.D . Univers ity of To ront o, Onta rio REFERENCES
Atkinson, L., Bevc, I., Dickens, S. & Blackwell , J. (in pre ss), Concur rent vali dities of the Stan ford-Bin et (Fourth Editio n), Lei ter, and Vi neland wit h deve lopme ntally delayed children. Journal ofSchool
Psychology. Fisher, G. M., Kilman, B. A. & Shortwe ll, A. M. (196 1), Comparability of inte lligence quotients of ment al defecti ves on the Wec hsle r Adult Intelli gence Scal e and the revision of the Stanford-Binet. J. Consult. Clin. Psychol., 25 :192-195. Knight , R. G. ( 1983), On interpreting the seve ral standard errors of the WAIS-R : some further tables. J. Consult. Clin. Psychol., 5 1:67 1-673. Spi tz, H . H . ( 198 8), In ver s e relati on sh ip bet ween th e WISC -RI WA IS-R score disparity and IQ level in the lower rang e of intelligence . Am. J. Ment. Defi c., 92:376-3 78. Strei ssguth, A. P., Rand els, S. P. & Smith, D. F. ( 199 1), A testretest study of intellige nce in patient s with fetal alcohol syndrom e: implications for care. J. Am. Ac ad . Child Adolesc. Psy ch iatry, 30:584-587.
The authors reply: Our rece nt art icle in the Journal was an attempt to share data from our cli nica l files with other cl inicians who have had little opportunity to exami ne childre n with Fetal Alcoho l Syndrome (FAS) or to see them over an extended period of their lives. We have been co ncerned about the discrepancy between the small number of reports in the scientific literature on group s of children with FAS , especially in co mpar ison with the magn itude of the probl em . Contrast this with autism, for example, to which an entire journa l is devoted , or eve n with much more esoteric groups of children with well-k nown psychiatric diagnoses, such as Tour ette ' s syndro me. Clinical data are never as pure as that obtai ned solely for research purposes, as Dr. Atki nso n po ints out. However , it is what clinicia ns deal with on a day -to-day basis in making decisions about thei r patien ts and in trying to help families under stand the problems they face in providin g for d isabled child ren across the life- span. The data in our article are pro babl y at least as goo d as that ava ilable to most clin icians in estima ting children's intellectual fu nctio ning . It is true that Test 1 and Test 2 were ofte n perform ed with di fferent tests-that is because neither the W ISC- R or the WAIS -R spans the ages represented in this rep ort. Furthermo re, when deali ng with patient s of such varied age s acr oss the life-span, it is inevitable that different stand ardization form s of the individual IQ tests have been employed.
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