0
Get Alert
Please Wait... Processing your request... Please Wait.
You must sign in to sign-up for alerts.

Please confirm that your email address is correct, so you can successfully receive this alert.

1
Letter to the Editor   |    
Letters to the Editor
ANTHONY DAVID, M.D., M.R.C.PSYCH.
Am J Psychiatry 1998;155:1626n-1626.
View Author and Article Information
London, U.K.

Letters to the Editor

To the Editor: Russell and colleagues have made an important contribution to the literature on intellectual functioning in patients with schizophrenia. However, their claim that intellectual decline is "a myth" overstates the case. The first problem is one that the authors partially acknowledge, namely, the biased nature of their study and, hence, the lack of generalizability. Their own data from a representative population-based cohort R5415511CHDDBHCI show that the premorbid IQ deficit in children who later develop schizophrenia is one-third of a standard deviation (i.e., around 5 IQ points). Equivalent figures from a later U.K. national cohort suggest that the deficit may be around one-half of a standard deviation (i.e., 8 IQ points) R5415511CHDDGFEJ, as do the data from the Swedish conscript cohort R5415511CHDDBAIA. The mean childhood IQ of their current group was 84.1, that is, just over one standard deviation below the mean. Hence, it is not representative of preschizophrenic children.

The next problem is the lack of control for a period effect, that is, changes in IQ in the population over time. Evidence from the United States shows that children’s intelligence has increased by approximately 3 points per decade since the 1930s R5415511CHDDEEJFR5415511CHDCFFJH, and anecdotal reports from the United Kingdom suggest similar trends in educational attainment. IQ tests standardized at the same time but employed years apart should reveal an increase.

In addition, research with groups with mild and moderate learning disability R5415511CHDDJIDGR5415511CHDCAHDI shows that subjects tested on the WISC and later on the WAIS (or their revisions) consistently show an apparent improvement due to psychometric properties of the scale, separate from the period effect. Hence, the lack of increase (or the slight decrease) in scores reported by Russell et al. masks a larger decrease in IQ over the follow-up period. Such a decrease is suggested by well-controlled, albeit cross-sectional, studies of first–onset cases R5415511CHDCDAGG in which schizophrenic patients’ cognitive measures are more than one to two standard deviations below the control mean.

Finally, a difficulty arises in the comparison of results from the WISC-R and the WAIS-R. Russell et al. quote correlation coefficients between the two scales, but this is misleading. There would be a perfect correlation between the scales even if one were consistently 10 points higher than the other. We need to know the slope of the regression line and its intercept.So what do we know for sure about IQ and schizophrenia? There is a slight reduction in the average IQ of children and young people who later develop schizophrenia. It is likely that there is a further reduction between childhood and the first onset of the disorder, although truly longitudinal data on this point are sparse. Whether there is a further deterioration in intellect in most cases over the course of the disorder is still an open question.

Jones P, Rodgers B, Murray R, Marmot M: Child developmental risk factors for adult schizophrenia in the British 1946 birth cohort. Lancet  1994; 334:1393–1402
 
Crow TJ, Done DJ, Sacker A: Childhood precursors of psychosis as clues to its evolutionary origins. Eur Arch Psychiatry Clin Neurosci  1995; 245:61–69
[PubMed]
[CrossRef]
 
David A, Malmberg A, Brandt L, Allebeck P, Lewis G: IQ and risk for schizophrenia: a population-based cohort study. Psychol Med  1997; 27:1311–1323
[PubMed]
[CrossRef]
 
Flynn JR: The mean IQ of Americans: massive gains 1932 to 1978. Psychol Bull  1984; 95:29–51
[CrossRef]
 
Richard L, Pagliari C: The intelligence of American children is still rising. J Biosoc Sci  1994; 26:65–67
[PubMed]
 
Rubin H, Goldman JJ, Rosenfeld JG: A follow-up comparison of WISC-R and WAIS-R IQs in a residential mentally retarded population. Psychol in the Schools  1990; 27:309–310
[CrossRef]
 
Avery RO, Slate JR, Chovan W: A longitudinal study of WISC-R and WAIS-R scores with students who are educable mentally handicapped. Education and Training in Mental Retardation  1989; 24:28–31
 
Spitz H: Inverse relationship between the WISC-R/WAIS-R score disparity and IQ level in the lower range of intelligence. Am J Ment Retard  1988; 92:376–378
[PubMed]
 
Vance HR, Brown W, Hankins N, Furgerson SC: A comparison of the WISC-R and the WAIS-R with special education students. J Clin Psychol  1987; 43:377–380
[PubMed]
[CrossRef]
 
Saykin AJ, Shtasel DL, Gur RE, Kester DB, Mozley LH, Stafiniak P, Gur RC: Neuropsychological deficits in neuroleptic naive patients with first-episode schizophrenia. Arch Gen Psychiatry  1994; 51:124–131
[PubMed]
 
+

References

Jones P, Rodgers B, Murray R, Marmot M: Child developmental risk factors for adult schizophrenia in the British 1946 birth cohort. Lancet  1994; 334:1393–1402
 
Crow TJ, Done DJ, Sacker A: Childhood precursors of psychosis as clues to its evolutionary origins. Eur Arch Psychiatry Clin Neurosci  1995; 245:61–69
[PubMed]
[CrossRef]
 
David A, Malmberg A, Brandt L, Allebeck P, Lewis G: IQ and risk for schizophrenia: a population-based cohort study. Psychol Med  1997; 27:1311–1323
[PubMed]
[CrossRef]
 
Flynn JR: The mean IQ of Americans: massive gains 1932 to 1978. Psychol Bull  1984; 95:29–51
[CrossRef]
 
Richard L, Pagliari C: The intelligence of American children is still rising. J Biosoc Sci  1994; 26:65–67
[PubMed]
 
Rubin H, Goldman JJ, Rosenfeld JG: A follow-up comparison of WISC-R and WAIS-R IQs in a residential mentally retarded population. Psychol in the Schools  1990; 27:309–310
[CrossRef]
 
Avery RO, Slate JR, Chovan W: A longitudinal study of WISC-R and WAIS-R scores with students who are educable mentally handicapped. Education and Training in Mental Retardation  1989; 24:28–31
 
Spitz H: Inverse relationship between the WISC-R/WAIS-R score disparity and IQ level in the lower range of intelligence. Am J Ment Retard  1988; 92:376–378
[PubMed]
 
Vance HR, Brown W, Hankins N, Furgerson SC: A comparison of the WISC-R and the WAIS-R with special education students. J Clin Psychol  1987; 43:377–380
[PubMed]
[CrossRef]
 
Saykin AJ, Shtasel DL, Gur RE, Kester DB, Mozley LH, Stafiniak P, Gur RC: Neuropsychological deficits in neuroleptic naive patients with first-episode schizophrenia. Arch Gen Psychiatry  1994; 51:124–131
[PubMed]
 
+
+

CME Activity

There is currently no quiz available for this resource. Please click here to go to the CME page to find another.
Submit a Comments
Please read the other comments before you post yours. Contributors must reveal any conflict of interest.
Comments are moderated and will appear on the site at the discertion of APA editorial staff.

* = Required Field
(if multiple authors, separate names by comma)
Example: John Doe



Related Content
Books
Dulcan's Textbook of Child and Adolescent Psychiatry > Chapter 11.  >
Dulcan's Textbook of Child and Adolescent Psychiatry > Chapter 14.  >
Dulcan's Textbook of Child and Adolescent Psychiatry > Chapter 11.  >
Dulcan's Textbook of Child and Adolescent Psychiatry > Chapter 11.  >
Dulcan's Textbook of Child and Adolescent Psychiatry > Chapter 12.  >
Topic Collections
Psychiatric News
APA Guidelines