Schizophrenia Research, 8 (1992) 69-73 0 1992 Elsevier Science Publishers B.V. All rights reserved

SCHIZO

69 0920-9964/92/$05.00

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Gender differences in cognition in schizophrenia Deborah

Perlick”,

Steven Mattis”,

Peter Stastnyb

and Jeanne

Teresi’

“Department of Psychiatry. New York Hospital-Cornell Medical Center, Westchester Division. White Plains, NY, bDepartment of Psychiatry, Albert Einstein College of Medicine. Bronx Psychiatric Center, Bronx, NY and ‘Research Division, Hebrew Home for the Aged at Riverdak, Riverdale. NY USA (Received

27 February

1992; revision

received

16 June 1992; accepted

22 June 1992)

Gender differences in cognition were investigated in schizophrenic inpatients and outpatients using the Dementia Rating Scale. Females displayed greater impairment on Attention and Conceptualization than males. Gender interacted with patient group for construction: females performed worse than males among inpatients and better among outpatients. Results may be related to the atypically early age of onset of females relative to males; attention to sampling and selection biases is needed in evaluating gender differences in cognition in schizophrenia. Key words: Cognition;

Gender

difference;

(Schizophrenia)

INTRODUCTION

Recent research on gender differences in neurocognition in schizophrenia has demonstrated greater structural brain abnormalities in males compared to females (Lewine et al., 1990; Josiassen, 1990; Andreasen et al., 1986) and more impairment among males on neuropsychological tests of verbal learning and fluency (Haas et al., 1991; Hoff et al., 1991). However, some studies have shown greater abnormalities or impairment on some measures among females (Nasrallah et al., 1990; Hoff et al., 199 I), and others have found no gender differences in cognitive functioning (Goldberg, 199 1). Reasons for the inconsistent findings may include differences between study samples in age of onset, chronicity, clinical course or other sampling biases. The present study investigated gender differences in neuropsychological functioning in two sociodemographically comparable groups of later-stageof-illness schizophrenic patients with divergent clinical courses, as part of a larger study of neuroCorrespondence to: Deborah Perlick, New York HospitalCornell Medical Center-Westchester Division, 21 Bloomingdale Road, White Plains, NY 10605, U.S.A.

and clinical characteristics of psychological patients with either long-term continuous community residence, or long-term inpatient status, previously reported in this journal (Perlick et al., 1992).

METHODS Selection of sample Subjects were 26 patients drawn from an urban state hospital (15 males, 11 females) and 26 patients (13 males, 13 females) drawn from two of its outpatient clinics. Inpatients had been hospitalized continuously for at least 18 months, and outpatients had resided in the community for three years or longer without rehospitalization. All patients met Research Diagnostic Criteria for chronic schizophrenia based on the Schedule for Affective Disorders and Schizophrenia (Spitzer et al., 1978), had a duration of illness of at least five years, and had been maintained on oral neuroleptic medication at a prescribed dose of at least 100 mg/day of chlorpromazine (CPZ) equivalents (Davis, 1974). Patients with Organic Mental Syndrome, history of electroconvulsive therapy, onset of psychiatric

70

illness (first admission) before age 16 or taking lithium carbonate or antidepressant drugs were excluded. Inpatients and outpatients were matched by group mean or frequency count for sex, ethnicity (white, nonwhite), socioeconomic status (SES), using the Hollingshead and Redlich (1958) twopoint scale, duration of illness (DOI) (5510, 10-l 5 and 15 plus years from first psychiatric admission) and age (within 5 yr). Analysis of the sample characteristics using two-tailed t tests or chi squares for categorical data demonstrated that the patient groups did not differ significantly by sex, SES, ethnicity or DOI (t = < 2.0, p > 0. lo), but that the matching procedure did not control for age; inpatients were on average 6.7 yr younger than outpatients (t= 2.74; df = 50; p < 0.01). Patient group characteristics and significant within-group comparisons are reported by gender in Table 1. The sample was on the whole representative of the more chronic and socioeconomically-deprived end of the schizophrenic spectrum. Most patients had been ill for over 10 yr and were from lower and lower middle class urban settings; about half were of minority extraction.

TABLE

Measures

In view of the reduced sample size when the inpatient and outpatient groups were subdivided by gender, the Dementia Rating Scale (DRS) (Mattis, 1989) was selected from the more comprehensive battery of neuropsychological tests used in the larger study (Perlick et al., 1992) to assess gender differences in cognitive functioning. The DRS was selected over other instruments because it provides a measure of overall cognitive functioning as well as more specific measures of functioning on five subscales (Attention, Memory, Initiation and Perseveration, Conceptualization and Construction), and has been found to detect differences on both overall and specific measures of cognitive functioning in different subgroups of schizophrenic patients (Cohen et al., 1988). The Pearson product moment correlation between the DRS total score and the composite measure of neuropsychological functioning described by Perlick et al. (1992) was 0.69 (df= 5 1; p < 0.0001); when corrected for attenuation (Nunnally, 1967), the correlation was 0.88. Because the DRS shared 77% of the variance with the composite measure of neuropsychological func-

1

Sample ckaractrristics Vuriahk

Age Age of onset BPRS total Serum CPZ equivalents

Race: %white SES: III, IV* V Duration of illness~ S-10 years** lo-15 years 15 + years

Inpatieni

Outpatient

Male in= 15)

Female Cn=lli

Male in=131

Female in = 13)

Mean (SD]

Mean (SD)

Meun (SD)

Mean

32.7(4.8) 19.9(3.6) 49.6(6.8) 672.7(604.2)

39.8(9.3)” 22.0(2.6) 58.0(7.2) 694.0(600.8)

42.8(11.6) 23.0(4.4) 47.8(12.9) 104.1(181.6)

(SD) 42.2(8.1) 24.0(4.7) 43.4(9.5) 35.9(27.7)

No. (%I

No. (Yo)

No. (%)

No. i%

6(40) 5(33) lO(67)

5(46) 406) 7(64)

7(54) 8(62) 5(38)

7(54) 6(46) 7(54)

6(40) 7(47) 2~3)

3(27) 5(46) 3(27)

3(23) 6(46) 4(31)

3(23) 7(54) 3(23)

J

a t/X2 < 0.05; other comparisons = NS. *SES rankings are derived from the Hollingshead Redlich Two Factor Scale: Hollingshead & Redlich, 1958. Since there was only one patient in each group ranked in the III category, these were combined with patients in the IV category for statistical analyses. **Duration of illness values refer to the number of years from the first psychiatric admission.

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tioning, its use as a measure representative of neuropsychological functioning in the study sample appeared justified. Ratings on the Brief Psychiatric Rating Scale (BPRS) (Overall and Gorham, 1962) made by one of two psychiatrists were used to assess the potential contribution of gender differences in symptom severity to gender differences in cognitive functioning. Statistics The presence of gender differences on the five DRS subscales was tested by two-way (sex x patient group) analyses of covariance (ANCOVA’s), covarying for age, and for BPRS total score and age of onset which were previously shown to differ between patient groups (Perlick et al., 1992). Multivariate techniques (MANCOVA) were not utilized because the assumption of common within-group covariance matrices for all groups (Bray and Maxwell, 1985, p, 33) was not met, i.e., the correlation coefficients between DRS subscale scores within the two patient groups differed appreciably in magnitude and in sign in several instances. In addition 8 of the 10 correlations between subscales for the total sample were not significant at the 0.05 level, and MANOVA may result in a Type II error when measures are largely uncorrelated and the sample size is relatively small (Bray and Maxwell, p. 12).

RESULTS Cognitive functioning Analysis of covariance revealed a significant main effect of gender for the DRS Conceptualization scale and a near-significant trend of gender for the DRS Attention scale (Table 2). For Conceptualization the comparison between men and women was borderline for inpatients (t= I .89, p< 0.08) and nonsignificant for outpatients. A significant gender by patient group interaction was found for the DRS Construction scale, with females scoring lower than males in the inpatient sample and marginally higher than males in the outpatient sample. There were no significant main or interaction effects observed for gender on the DRS Memory or Initiation and Perseveration scales. Consistent with findings reported by Perlick et al. (1992)

significant main effects for patient group were obtained for the Attention, Memory and Initiation and Perseveration scales. With respect to gender, these findings demonstrate more impaired verbal and nonverbal abstracting ability, concept formation, visual scanning, sustained attention and self-monitoring in female relative to male chronic schizophrenics. They also indicate greater impairment in memory and attentional processes, in verbal fluency and in motor and graphomotor sequencing in inpatients relative to outpatients. In order to evaluate the overall level of cognitive impairment of the study sample relative to normal adults, we used data reported by Butters et al. (1985) for normal controls (2 age= 51; n = 14) attaining a DRS total score of 141 f2.8. Patients scoring < 135 on the DRS total score (at least 2 standard deviations below the mean for normal controls) were considered to manifest at least mild cognitive impairment. Based on this criterion, 85% of inpatients (87% M, 82% F) and 73% of outpatients (69% M, 77% F) exhibited a mild or greater degree of cognitive impairment.

DISCUSSION

The variable pattern of neuropsychological performance of female relative to male schizophrenics found in this study, with greater impairment for females on measures of conceptualization and attention, no gender differences on measures of memory or initiation and perseveration and an interaction of gender with patient group for constructional ability, underscores the complexities involved in the study of gender differences in cognition in schizophrenia. The results of the study need to be interpreted within the frame of the sampling strategy employed and the specific characteristics of the sample. Because the sampling procedure was designed to equate patient groups on age and duration of illness, differences in age of onset both between patient groups and between males and females were also minimized. Thus, in contrast to work demonstrating that female schizophrenics typically have a later age of onset than males (e.g., Anger-

12 TABLE

2

DRS cognitive impairment: patient group by gender DRS Subscale

Inpatienr Male

Attention Memory Conceptualization Initiation & Perseveration Construction Total score

Ouiputient Female

Male

F Value Female

Group

Se.u

ht.

35.3(1.9) 21.5(3.0) 36.5(4.1)

33.6(2.9) 18.8(4.1) 32.5(5.5)

35.9(1.8) 22.2(2.6) 36.5(3.4)

35.6(0.9) 22.5(2.3) 34.0(6.9)

9.63d 4.95’ 0.42

3.21” 1.85 4.57’

l.U9 2.19 0.10

28.9(5.7) 6.0(0.0) 127.5(10.2)

29.3(5.2) 5.8(0.6) 119.9(12.2)

31.9(3.0) 5.8(0.6) 132.4(5.4)

32.8(3.8) 5.9(0.6) 130.3(7.4)

3.95b 0.24 _

0.01 0.49

0.14 4.01b

“piO.10. bp=O.O5. cp

Gender differences in cognition in schizophrenia.

Gender differences in cognition were investigated in schizophrenic inpatients and outpatients using the Dementia Rating Scale. Females displayed great...
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