Specificity of the Calgary Depression Scale for schizophrenics

Schizophrenia Research, 11 (1994)239-244 0 1994 Elsevier Science Publishers B.V. All rights reserved

SCHRES

239 0920-9964/94/$07.00

00333

Specificity of the Calgary Depression Scale for schizophrenics Donald

Addington”,*,

Jean Addingtonb

and Eleanor

Maticka-Tyndale”

“Department of Psychialry, University of Calgary, Foothills Hospital 1403 29 St NW, Calgary, Alberta, Canada T2N 2T9 and bDepartment of Psychiatry.University of Calgary, Holy Cross Hospital, 2210 2nd Street SW, Calgary Alberta, Canada T2S IS6 (Received

10 October

1992; revision received

19 March

1993; accepted

5 April 1993)

This study sought to determine the specificity of the Calgary Depression Scale (CDS), a depression rating scale for schizophrenics. The specificity is the degree to which the scale assesses depression rather than negative or extrapyramidal symptoms. Subjects were 100 outpatients (OP) and 50 inpatients (IP) meeting DSM-III-R criteria for schizophrenia. Negative symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS); extrapyramidal symptoms were assessed with the Simpson Angus Scale (SA) and depression with the CDS. Results were that the CDS showed no correlation with SA, but weak (0.33) statistically significant correlations with the PANSS negative symptom score in inpatients but not outpatients. Confirmatory factor analysis using Lisrel 6.0 showed that the model hypothesizing specificity of depression, negative symptoms and extrapyramidal symptoms, was significant, with a goodness of fit index of 0.89 and a root mean square residual of 0.07. It is concluded that the CDS achieves a useful degree of separation between measures of depression, negative and extrapyramidal symptoms in subjects with schizophrenia, when combined with the other measures used in this study. Key words; Depression;

Rating

scale; Negative

symptom;

Extrapyramidal

INTRODUCTION

This study is the third in a series of studies to develop and test the Calgary Depression Scale (CDS), which has been designed as a measure of level of depression in schizophrenia. The CDS was originally derived by factor analysis from two widely used depression rating scales in order to exclude symptoms of schizophrenia which do not factor together with depression in schizophrenia (Addington et al., 1990). In a second study the CDS has been shown to have high interrater reliability, high internal reliability and validity (Addington et al., 1991). Validity was established by three criteria: the ability of the scale to predict the presence of a major depressive episode; correlation of the scale with

*Corresponding SSDI

author.

0920-9964(93)E0034-Q

symptom;

(Schizophrenia)

other depression measures; and confirmatory factor analysis. The present study was designed to assess the specificity of the CDS, that is the degree to which it measures level of depression rather than negative or extrapyramidal symptoms. The distinction between negative, depressive and extrapyramidal symptoms has become increasingly important in light of the search for biological correlates of the negative syndrome (Walker and Lewine, 1988). Considering both the potential response of depression to antidepressant medication (Siris et al., 1987) and the search for pharmacological treatments for negative symptoms (Meltzer, 1991) there are important clinical implications to determining these distinctions. The problems of distinguishing depression, negative symptoms and akinesia have been reviewed in detail (de Leon et al., 1989). While some studies have found that measures of depression and negative symptoms overlap (Craig et al., 1985; Prosser

240

et al., 1987; Addington and Addington, 1989; Kulhara et al., 1989), other studies have not found an overlap (House et al., 1987, Barnes et al., 1989, Hirsch et al., 1989). A number of reasons can be found to account for the discrepant findings in the literature. First, there is the lack of an adequate scale for assessing depression in schizophrenic populations (Craig et al., 1985, Addington and Addington, 1989). Secondly, there is a lack of agreement on the definition of negative symptoms (De Leon et al., 1989). The studies finding no overlap have used narrower scales, using scores for negative symptoms based on only a few items of a scale such as the behavioral items of the PSE (House et al., 1987) or the negative symptom score of the BPRS (Newcomer et al., 1990). Broader definitions such as the Scale for Assessment of Negative Symptoms (Andreasen, 1982) lead to significant overlap (Addington and Addington, 1989, Kulhara et al., 1989). Thirdly, different methods of data analysis have been used. Whereas some studies have examined correlation coefficients between total depression scale scores and total negative item scores 1990) or between total (Newcomer et al., depression scores and individual negative item scores (Addington and Addington, 1989) others have compared frequency of negative and extrapyramidal symptoms in depressed and non-depressed patients (Hirsch et al., 1989). Finding that depressed subjects do not have more negative symptoms than non-depressed subjects is evidence against a serious confounding of the two concepts, but does not disprove some overlap. Similar to the overlap between depression and negative symptoms the results of studies which examine the overlap between depression and extrapyramidal symptoms are affected by the choice of measures used and the methods of data analysis. Overlap has been reported in some studies (Rifkin et al., 1975; Van Putten and May, 1978; Craig et al., 1985; Prosser et al., 1987) but not others (Barnes et al., 1989; Hirsch et al., 1989). The goal of the present study was to demonstrate that the CDS, when combined with two widely used measures of negative and extrapyramidal symptoms, would achieve a useful degree of separation between depressive, negative and extrapyramidal symptoms.

METHODS

This was a cross-sectional study on a different sample of schizophrenic subjects from the study of reliability and validity of the CDS (Addington et al., 1992). Each subject was assessed on measures of depression, extrapyramidal and negative symptoms. The Calgary Depression Scale (CDS) was the measure of depression, the Positive and Negative Syndrome Scale (PANSS) (Kay et al., 1987) the measure of negative symptoms. The PANSS was selected because its negative scale is part of a comprehensive assessment of psychopathology and is able to assess change. The Simpson Angus Scale (SA) (Simpson et al., 1966) was used as a measure of extrapyramidal symptoms. Subjects included both inpatients and outpatients in order to sample a wide range of psychopathology. Subjects were assessed independently by one rater on the level of depression using the CDS, and by another independent rater on measures of negative and extrapyramidal symptoms. Interrater reliability was established on all measures by joint interviews with the PI and the research assistants. After a number of training sessions both the PI and the research assistant alternated interviewing and observing during the assessment of 10 subjects, 5 inpatients and 5 outpatients. The intraclass correlation coefficients were 0.97 for the PANSS negative scale, 0.96 for the CDS, and 0.63 for the Simpson Angus. The principal analytical step in establishing the specificity of the CDS as distinct from measures of negative and extrapyramidal symptoms is confirmatory factor analysis (CFA). In such an analysis, items on each scale are constrained to load only on their respective dimensions. The fit of the data to such a model indicates whether the condition of specificity is met with no statistically significant variance left unexplained. Three analytical steps were taken prior to the confirmatory factor analysis to establish whether the scales, as used with this population, were suitable for CFA. (1) The variance of scores of both inpatients and outpatients on each scale were examined to determine whether these met the assumption of normal distribution required in the factor analytic procedure. Where necessary, adjustments were made.

241

(2) Chronbach’s alpha was used to assess the internal consistency of items for each scale. (3) Frequency distributions of negative symptoms for patients scoring above and below the CDS cut point of 6 were plotted to provide for a visual portrayal of the independence of severity of negative symptoms from depression. (4) Because they are commonly used as summary illustrations of the closeness of association between scores on symptom measures, Pearson product moment correlations were calculated for inpatients and outpatients separately.

Scale

Pos Neg GPS SA CDS

reliability

of all scales Coejficient Scale

alpha

0.84 0.76 0.54

toms in depressed and non depressed subjects is presented in Fig. 1. In order to assess the relationship among the different symptoms, correlations between depression, negative and extrapyramidal symptoms were assessed using Pearson Correlations. Correlations involving the CDS were calculated using PRELIS 1.9 (Joreskog et al., 1986) because the CDS frequency distribution showed an extreme positive skew and was considered to be a censored normal distribution. The results of these correlations are presented in Table 3. In order to further explore the source of the correlations between the CDS and PANSS, correlations between the total CDS and individual PANSS negative symptoms were examined for the combined sample of 150. The results are presented in Table 4. Finally, to assess whether the items on the three scales were distinct enough that they could be considered to measure three separate, though clinically overlapping, symptom clusters, a confirmatory factor analysis was conducted. The LISREL statistical package was used with Pearson product moment correlations (identifying CDS as censored

RESULTS

Symptom

Internal

Calgary Depression PANSS Negative Simpson Angus

Two groups of patients were assessed. First, a group of fifty acutely ill hospitalized patients with schizophrenia who had high levels of symptoms. Second, a group of 100 outpatient schizophrenics with fewer symptoms. The two groups differed on negative and depressive measures of positive, symptoms but not on measures of extrapyramidal symptoms. Both inpatients and outpatients showed variance in levels of symptoms, as indicated by similar standard deviations despite differences in the mean levels of symptoms (Table 1).

TABLE

2

Scale

Sample

Internal reliability on all scales was good for the Simpson Angus Scale (Table 2). The frequency distribution of negative

TABLE

except symp-

1 comparisons

between schizophrenic

Range

In patients

7-49 7-49 16-112 O-38 O-27

inpatient and outpatient

groups

Out patients

x

(SD)

x

(SD)

21.3 21.8 38.5 5.1 4.9

(6.0) (5.3) (9.6) (2.9) (4.5)

13.0*** 1s.5*** 29.8*** 5.6 3.3*

(5.39) (4.38) (6.48) (3.24) (4.06)

Significance of the differences in mean symptom levels between schizophrenic outpatients and inpatients: *p
242 %N 25

,,-,2

m-,4

,s-,*

IT-,*

,e-*o

*I-P*

28-P.

**-2*

*I-*8

28.

negative score Fig. 1. Depressed

TABLE

vs non-depressed,

CDS > 6 vs CDS < 7. Distributions

3

Pearson correlations PANS.9 Neg

Group Inpatients n = 50 PANSS Neg CDS a SA Outpatients n = 100 PANSS Neg CDS a SA Total group n = 150 PANSS Neg CDS a SA “CDS treated as censored *p
TABLE

CDS”

_ 0.33* 0.35**

_ 0.17

distribution

4

and outpatients

Blunted affect Emotional withdrawal Poor rapport Passive apathetic withdrawal Difficulty in abstract thinking Lack of spontaneity Stereotyped thinking Total negative score *p
**p
normal), and maximum likelihood estimation procedures. A model hypothesizing specificity of depression, negative and extrapyramidal items was estimated. The estimated standardized coefficients for each item are presented in Table 5. The goodness of fit statistics are presented in Table 6.

0.01

0.27*’ 0.22

negative items

p < 0.05.

DISCUSSION

0.18 0.19

Depression and negative symptoms Correlations between depression and negative items in inpatients

PANSS

different,

0.17

_

normal

significantly

Correlation 0.19* 0.30** 0.22* 0.33** 0.01 0.07 0.07 0.28**

with CDS

The sample of patients assessed represent a wide range of severity and type of schizophrenic psychopathology, including positive, negative and depressive symptoms. Such a range allows the results obtained to be generalized to a broad range of clinical populations. The main finding of the study is that the CDS achieves a good level of separation between level of depression, negative symptoms and extrapyramidal symptoms in this sample of both inpatients and outpatients with schizophrenia. In the outpatient group there is no evidence of overlap between either depression and negative symptoms or between depression and extrapyramidal symptoms. In the inpatient sample there is again no evidence for overlap between depression and extrapyramidal symptoms. The statistically significant correlation between the CDS and negative symptoms in the inpatient sample can be interpreted in two ways. The first possibility is that the correlations observed in the

243

TABLE

S

Standardized coefficients for

bestfitting model CDS-PANSS Neg-SA (Lisrel6.0

Item

Negative symptom

Blunted affect Emotional withdrawal Poor rapport Passive Abstract thought Lack spontaneity Stereotypic thought Gait Arm dropping Major joints Cogwheeling Glabella tap Tremor Salivation Akinesia Akathisia Depressed mood Hopelessness Self depreciation Guilty ideas of reference Pathological guilt Morning depression Early wakening Suicide Observed depression

0.86 0.55 0.79 0.53 0.32 0.51 0.28

*Non-significant

TABLE

coefficients.

Extrapyramidal

Lambda matrix) Depression

0.54 0.55 0.57 0.68 0.16* 0.31 0.1s* 0.27 0.06* 0.83 0.85 0.70 0.30 0.37 0.59 0.26 0.63 0.81 All other coefficients

in the table are significant

6

Goodness ofjit statistics for conJrmatory factor analysis CDS-SA-PANSSNeg Chi Square Degree of freedom Probability p Goodness of fit index Root mean square residual Toal coefficient of determination

244.170 253 0.643 0.893 0.070 0.986

acute stage represent the simultaneous increase in global psychopathology associated with relapse (Knights and Hirsch, 1981; Green et al., 1990; Addington and Addington, 1991). Thus, the significant relationship between the scores on negative symptoms and on the CDS may be due to their mutual association with relapse, rather than to an association with each other. From this perspective the observed correlations would be considered a spurious effect. The second possibility is that the

at p < 0.05 (most p < 0.01).

correlation may represent a confounding of depression and negative symptoms, that is, a measurement problem. The CDS may be assessing, to a degree, levels of negative symptoms. This is not supported by the confirmatory factor analysis. Instead the confirmatory factor analysis shows strong support for the hypothesis that the CDS, PANS& and SA measure separate constructs. Confirmatory factor analysis offers a powerful statistical technique for addressing the problem of differentiating depressive and negative symptoms in the absence of definite biological correlates of these syndromes. This study, combined with the study of reliability and validity of the CDS (Addington et al., 1992), demonstrates that the CDS possesses a number of important features. The CDS is a valid measure of depression, which has both high internal reliability and good interrater reliability. It is sensitive to change and is suitable for both inpatients and outpatients. Furthermore all of its items predict the presence of a major depressive episode. Finally, the present

244

study indicates that the CDS is a good measure for attempting to measure depression separately from negative and extrapyramidal symptoms.

ACKNOWLEDGEMENTS

This research was supported R03 MHZ 48671-01.

by NIMH

grant No. 1

REFERENCES

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