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DEPRESSION AND ASSESSMENT OF INTELLECTUAL FUNCTIONING WILLIAM W . HALE 111, PETER DINGEMANS, ELLIE WEKKING A N D EVERT CORNELISSEN

Academic Medical Center Amsterdam, The Netherlands

This study examined the relation between WAIS and Wilson predictor of premorbid intelligence scores of 27 depressed and 34 nondepressed psychiatric patients. No significant difference was found between the WAIS and Wilson predictor of premorbid intelligence scores nor between the Verbal and Per- formance IQs.

Tests of a patient’s intellectual functioning are well-integrated components of psychiatric test batteries (Kaplan & Sadock, 199 1). Wechsler Adult Intelligence Scale (WAIS) findings are used in the differential diagnosis and interpretation of psychological dysfunctions, disorders, and syndromes (DSM-111-R; American Psychiatric Association, 1987).

While a great body of research has been devoted to the study of intellectual func- tioning of depressed patients, the findings of these studies are inconsistent. For example, Pernicano’s study (1986) found that the Verbal IQs of depressed patients were generally 15 or more points more than their Performance IQs. This finding has been confirmed in studies by Brumback (1985) and Hart and Kwentus (1987). Conversely, Mokros, Poz- nanski, and Merrick (1989) and Gass and Russell (1986) found no relation between Verbal and Performance IQs of depressed patients. Donnelly, Murphy, Goodwin, and Waldman (1982), Correll (1985), Clark et al. (1985) and Weiner and Pfeffer (1986) found little support for a relation between intellectual functioning and severity of depression.

The present research further explores whether the intellectual functioning of depressed patients is affected negatively by their depression.

Correspondence should be addressed to Peter Dingemans, Academic Medical Center, Department of Psychiatry, Tafelbergweg 25, 1105 BC Amsterdam-Zuidoost, The Netherlands.

774 Journal of Clinical Psychology, November 1993, Vol. 49, No. 6

METHOD

Subjects Consecutively referred psychiatric ambulant and inpatients who consented to par-

ticipate took part in this study. Patients with organic mental disease and those referred for neuropsychological testing were excluded.

A final sample of 61 patients remained. This sample was composed of primarily ambulant patients (67.2%), aged 18 to 65 years (M = 33, SD = 1 l), who did not receive neuroleptic treatment (91.8%). There were 33 males (54.1 To) and 28 females (45.9%) in the sample. The mean educational background was of a junior college level (M = 13.6, SD = 3.9).

The patients were classified into two diagnostic (DSM-III-R) groups: depressed (n = 27) and nondepressed (n = 34). The depressed group consisted of major depression (n = 22), dysthymia (n = 4), and depressive disorder NOS (n = 1). The nondepressed group was a heterogeneous grouping of psychiatric patients (e.g., anxiety disorders, psychotic disorders).

Measures The patients were assigned a DSM-III-R diagnosis by their treating psychiatrist.

In addition, each patient was interviewed by an independent clinical psychologist with the Brief Psychiatric Rating Scale (BPRS; Overall & Gorham, 1976). The Dutch version of the WAIS was used in the measurement of the patient’s intellectual functioning (Stinissen, Willems, Coetsier, & Hulsman, 1970). The Wilson predictor of premorbid intelligence (Karzmark, Heaton, Grant, & Matthews, 1985; Wilson, Rosenbaum, & Brown, 1979; Wilson et al., 1978) was employed for the determination of the patient’s premorbid intelligence.

The Wilson predictor arrives at its estimate of a person’s premorbid intelligence based on the following equation: Full Scale IQ: .17 (age) - 1.53 (sex) - 11.33 (nationality) + 2.97 (education) + 1.01 (occupation) + 74.05.

Procedure In addition to regular psychological diagnostic testing, a standardized Full Scale

WAIS was done by each patient. Then, a short interview for the completion of the Wilson predictor of premorbid intelligence was conducted. The patients’ BPRS scores and diagnoses were collected from the testing file and the clinical discharge notes.

RESULTS

The distinction between the clinical diagnosed groups was confirmed by a com- parison of the factor scale scores of the BPRS across groups, which showed a significantly higher score on the depression factor in the depressed group, F(1,52) = 9.9, p -c -001, than in the nondepressed group. Groups did not differ in their estimated and observed IQs and BPRS total score. Therefore, we did not use the BPRS total score as a covariant in further analyses. Age was the only other significant difference between the groups, F(1,60) = 6.0, p I .05; depressed (A4 = 37, SD = 11.5) and nondepressed (M = 30.5, SD = 8.9). There were no significant differences between the WAIS and the Wilson predictor in both groups and between groups. Diagnostic groups could not be discriminated on WAIS subtest scores.

In accordance with the Morkos and Brumback studies, patients were classified in groups with regard to verbal and performance discrepancies of 15 or more IQ points. These discrepancies were compared across the depressed and nondepressed groups. The depressed and nondepressed groups could not be differentiated in regard to verbal and performance discrepancies.

Depression and Intelligence 775

Table 1 Mean WAIS and Wilson Predictor Scores of the Depressed and Nondepressed Groups

WAIS Wilson

Depressed

Nondepressed (n = 27) 114 (19SD) 1 1 1 (14SD)

(n = 34) 112 (17SD) 109 ( 1 4SD)

Note.-r-test results were not significant.

Table 2 Found performance IQ and Verbal IQ Diyerences of I5 Points or More in the Groups of the Current Study, Brumback (1985), and Mokros, Poznanski, and Merrick (1989)

P < V P = V V < P Total ~~ ~

Current study Depressed 2 (7%) 18 (67%) 7 (26%) 27 Nondepressed 4 (12%) 27 (80%) 3 (8%) 34

Depressed 3 ( 1 1 % ) 22 (82%) 2 (7%) 21 Nondepressed 0 (0%) 13 (87%) 2 (13%) 15

Mokros (1989)

Brumback (1985) Depressed 21 (34%) 23 (38%) 17 (28%) 61 Nondepressed 5 (14%) 24 (67%) 7 (19%) 36

Note.-P = Performance IQ. V = Verbal IQ.

Correlation analyses revealed a strong correlation between the WAIS and the Wilson predictor in both the depressed ( r = .70, p < .001) and nondepressed (r = .79, p < .001) groups. Moreover, correlations between the Verbal IQ and the Wilson predic- tor (depressed: r = .69, p < .001; nondepressed: r = .79, p < .001) were stronger than the correlations between the Performance IQ and the Wilson predictor (depressed: r = .56, p < -001; nondepressed: r = .64, p < .001).

Correlation analyses within the depressed and nondepressed groups were done. For the depressed group, a distinction was made between the major depression single episode and recurrent categories. Dysthymia and Depressive disorder NOS were not included due to small group sizes. The nondepressed group was subdivided into psychotic and neurotic categories. The correlation between the WAIS and the Wilson predictor for the depression categories was comparable with the depressed group: major depression, single episode (r = .78, p < .001); major depression, recurrent (r = .71, p < .01). The correlation between the WAIS and the Wilson predictor rose strongly in the psychotic group (r = .90, p < .001) and remained stable in the neurotic group (r = .77, p < .001).

Regression analyses showed that WAIS Total (B = 3.3, R2 = .52), Verbal (B = 3.0, R2 = .51) and Performance (B = 2.7, RZ = .34) IQs of the depressed group were best indicated by the education variable, whereas the Wilson predictor was the best indicator of the nondepressed group’s WAIS Total (B = .96, R2 = .61), Verbal (B = .92, R2 = .65), and Performance (B = .79, R2 = .44) IQs.

DISCUSSION

The means and the correlations between the WAIS Full Scale IQ and Wilson predic- tor indicate in this study that depression exerts little effect on the depressed patient’s ability

116 Journal of Clinical Psychology, November 1993, Vol. 49, No. 6

to perform at premorbid levels. Diagnostic groups, and subgroup categories, could not be discriminated on the basis of verbal and performance discrepancies. Differences of 15 or more points were primarily in favor of Performance IQ in the depressed group. Thus, the findings of the aforementioned research that the Verbal IQs of depressed patients are generally 15 or more points more than their Performace IQs are not sup- ported by this study.

Possible limitations of this study were detected in the review of the analyses of variance and regression. The age difference between the depressed and nondepressed groups was significant, however, the WAIS raw test scores were calculated in respect to the patient’s age and sex. It is, therefore, unlikely that age differences between the groups affected the findings.

In future studies, consideration should be given to longitudinal study. Psychiatric patients generally are tested after a certain stability in their clinical status has been at- tained. Longitudinal study of the intellectual functioning of depressed patients with IQ tests performed before such stability occurs would provide insight into whether this is a confounding factor. It was also interesting to note that the education variable turned out to be a better predictor of the depressed group’s WAIS scores than the Wilson predic- tor. The use of the education variable for estimation of premorbid intellectual func- tioning also should be explored further.

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