Schizophruniu Reseurch, 8 (I 992) 143- 156

0 1992 Elsevier Science Publishers B.V. All rights reserved 0920-9964/92/$05.00

143

SCHIZO 00258

Positive and negative symptoms in the psychoses: Multidimensional scaling of SAPS and SANS items

I.H. Minasasbv G.W. StuarPb, S. Klimidis”sh, H.J. Jackson’, B.S. Singhb- and D.L. Copolovb

’ Victorran Transcultur-al Psychiatry Unit, Victor@ Australia; and bTht~ National Health & Medical Research Cowwil Schizophrenia

Research Unit, Royal Park Hospital, Parkvillr. Victoria. Australia.

(Received 20 January 1992: revision received 9 June 1992; accepted 9 June 1992)

Recently, the validity of the simple dichotomy between positive and negative symptoms in psychosis has been questioned. A newly admitted group of 114 DSM-III patients with psychotic disorder were assessed using Andreasen’s positive and negative symptom scales. Multidimensional scaling, augmented by cluster

analysis, was applied to the full item set of these scales and showed clearly that there are three major, independent groups of symptoms: Hallucinations/Delusions, Positive Thought Disorder and Negative

Symptoms. Within the Hallucinations/Delusions and Negative Symptoms groups there was some additional structure which does not conform to the SAPS and SANS sub-scales. In particular there was considerable heterogeneity within the Hallucinations/Delusions group, and delusions of persecution may represent a fourth independent dimension of psychopathology which is under-represented in these scales.

Ke), ~vordr; Multidimensional scaling; Positive and negative symptoms; Psychosis; (Schizophrenia)

INTRODUCTION

In recent years research on schizophrenia has increasingly focused on positive and negative symptoms. The distinction between the two symp- tom types was initially based on clinical phenome- nology. A contrast was made between positive or productive symptoms, such as hallucinations, delu- sions and positive thought disorder, and negative symptoms which were regarded as deficits in nor- mal functioning, such as affective flattening, voli- tional impairment and ideational deficits. There has been, however, some disagreement concerning the allocation of individual symptoms to the posi- tive or negative groups (Walker and Lewine, 1988). Initially, interest centred on the issue of whether positive and negative symptoms should be viewed as mutually exclusive or independent syndromes

Correspondence to: I.H. Minas, Victorian Transcultural

Psychiatry Unit, II0 Nicholson St, Fitzroy, Victoria, 3065,

Australia.

(Andreasen and Olsen, 1982; Crow, 1982, 1985;

Kay and Opler, 1987) rather than on any possible heterogeneity within the two symptom classes.

External validation of the distinction between

negative and positive symptoms has come from

studies of the relationship between symptoms and

medication response (Johnstone et al., 1978; Angrist et al., 1980; Mackay, 1980), longitudinal

course (Pfhol and Winokur, 1982) ventricular

enlargement (Andreasen and Olsen, 1982;

Andreasen et al., 1982) brain metabolism (Franzen

and Ingvar, 1975; Ingvar, 198 I; Volkow et al., 1987) and neuropsychological performance (Owens and Johnstone, 1980; Green and Walker,

1985; Kemali et al., 1985). These studies essentially treated the positive and negative symptom com- plexes as unitary constructs without exploring whether or not particular symptoms (or symptom subgroups) within each symptom complex are

specifically associated with external measures. Studies which have further explored relations

between external measures and subgroups of symp-

144

toms within the two broader classes have been

few. However, they have been suggestive of further

valid subdivisions within, in particular, positive

symptoms. Bilder et al. (1985) for example, indi-

cated that neuropsychological performance deficits were associated with only some of the positive

symptoms-those clustering around the construct

of thought disorder (including alogia). Similarly,

Liddle (1987a) noted different neuropsychological

deficits were associated with different positive

symptom complexes-delusions and hallucina-

tions were correlated with figure-ground resolution impairments while a syndrome comprised of posi-

tive thought disorder and inappropriate affect was

correlated with impairments in visual selection and tracking, visuospatial memory and word recogni-

tion memory. Kulkarni et al. (1990) noted a rela-

tionship between haloperidol-stimulated prolactin

release and the severity of delusions, suggestive of

a specific link between delusions and dopaminergic

overactivity.

The development of reliable scales for the meas-

urement of positive and negative symptoms, such as the Scale for the Assessment of Positive Symp-

toms (SAPS) and the Scale for the Assessment of

Negative Symptoms (SANS) (Andreasen, 1983, 1984) has enabled significant advances in such

work. However, the general acceptance of the

SAPS and SANS by researchers has somewhat out-paced the comprehensive evaluation of their

psychometric properties. In the development of the SAPS and SANS (Andreasen, 1982; Andreasen

and Grove, 1986) sub-scales were validated by

demonstrating internal consistency within the sub-scales, using Cronbach’s alpha and item-total correlations. Correlations between items from different sub-scales were not reported. When

internal consistency techniques were applied to the SANS, it was found that each sub-scale had an acceptably high alpha coefficient, although each item seemed to correlate only slightly better with its own sub-scale score than it did with the total negative symptom score. Andreasen and Grove (1986) interpreted such a slight reduction in corre- lation as indicative of the validity of the sub-scales, since any reduction in the correlation would indi- cate that additional variance is explained by the item. The possibility that a negative scale item might correlate more highly with symptoms in

other sub-scales of the SANS, or with symptoms in the SAPS, was not explored.

In the case of the SAPS, there was a bigger difference between ‘item to sub-scale’ and ‘item to total score’ correlations (Andreasen and Grove, 1986) indicating that the sub-scales add informa- tion to that which may be derived from the total score. However, many items did not correlate well with their own sub-scale scores. For example, all delusions were grouped together regardless of type, but many of these were not highly correlated with the sub-scale (sum of items) score for delusions and were also very poorly correlated with global ratings of delusions. This could be due to the possibility that these items are not measuring the same underlying construct or it may reflect the wide variation in symptom base rates, as reported in Andreasen (1987). It has therefore been difficult to determine the degree to which this internal consistency analysis actually supports the structure of the scales.

Given these ambiguities. it has been unclear whether more than two underlying dimensions are

measured by the Andreasen scales. A more appro- priate way to approach the problem is to examine inter-item correlations for the total item pool.

Although Andreasen and Olsen (1982) and Andreasen and Grove (1986) did carry out princi- pal components analyses, leading Andreasen and Olsen (I 982) to suggest that ‘the group of positive symptoms may represent more than one symptom complex’ (p. 793) these were done using the global ratings rather than individual item ratings. The results of these two analyses were inconsistent with each other, although both yielded four factors. Andreasen and Grove (1986) found that the nega- tive symptoms were spread across two separate factors while Andreasen and Olsen (1982) found that all negative symptoms loaded on a single factor together with hallucinations and delusions which were negatively loaded on this factor. Kulhara et al. (1986) also carried out a principal components analysis of the global ratings of the SAPS and SANS and obtained a simpler solution, with all the negative symptoms loading onto a single factor, hallucinations and delusions on a second, and bizarre behavior and formal thought disorder on a third. Andreasen and Grove (1986) also found delusions and hallucinations to load together on a separate factor from the remaining

145

positive symptoms. The structure found by Kulhara et al. (1986) is very similar to that derived by Bilder et al. (1985) Simpson and Davis (1985) Liddle (1987b) and Arndt et al. (199 l), all of whom used exploratory factor analytic rather than con- firmatory methods. These studies, which have used a variety of measurement scales and different samples, clearly suggest that the two-syndrome model is an inadequate representation of the range of psychotic symptoms measured by the SAPS and SANS and by other instruments.

The aim of this study was to determine the number, and characteristics, of dimensions

required to adequately account for the common variance in the SAPS and SANS set of items. No previous study of the SAPS and SANS has exam- ined the dimensionality of the complete set of items. The studies referred to above have generally studied small samples of psychotic patients, have used global SAPS and SANS measures or have used different scales. In the process of exploring this issue the present study examines the adequacy of the subscale composition and structure of SAPS and SANS. It does this by use of correlational methods, since confirmatory methods will always yield some support for an a priori clustering of symptoms unless the pre-determined groupings are completely invalid. The analysis was based on the technique of multidimensional scaling, augmented by cluster analysis of variables. These techniques can be used to explore the structure of a correlation matrix without restricting it to particular clusters of items, nor requiring that these clusters represent independent dimensions (as in the case of ortho- gonal factor analysis). Multidimensional scaling has the advantage that it is a graphical technique which represents the correlation matrix as a ‘map’ which is then open to interpretation.

Positive and negative symptoms are common in psychotic disorders other than schizophrenia (e.g., Pope and Lipinski, 1978; Sommers, 1985) and the boundaries between schizophrenia and other psychotic disorders remain unclear (Andreasen, 1987). In the study of positive and negative symp- toms it would seem that a narrow focus on schizo- phrenia is premature and will perhaps provide only a limited view of the relationship between positive and negative symptoms. This study therefore included a diagnostically heterogeneous sample of psychotic patients.

METHODS

Sut7jects and procedure One hundred and fourteen patients with DSM-III (American Psychiatric Association, 1980) diagno- ses of psychotic disorder formed the sample. Diag- nostic information was elicited using the Royal Park Multidiagnostic Instrument for Psychoses (McGorry et al., 1990a,b). This instrument has been shown to have adequate diagnostic reliability

(McGorry et al., 1990b). All subjects, following explanation of the aims and procedures of the study, gave written and witnessed consent to parti- cipation. The sample consisted of consecutive admissions to the research ward of a metropolitan psychiatric hospital, with admission conditional upon meeting both inclusion (age between 15 and 45 and clinical presentation suggestive of the presence of psychotic disorder) and exclusion (DSM-III diagnosis of organic mental disorder, mental retardation and inadequate English fluency) criteria. Table 1 presents demographic and illness characteristics of the sample by DSM-III diagnostic category.

Interval and ordinal scale variables in Table 1

were analysed using one-way analyses of variance, whilst frequency variables were analysed using the

X2 statistic. When significant differences were found, the Scheffe post-hoc procedure (with an alpha of 0.10, Scheffe, 1959) was used to determine which groups significantly differed from the others. These analyses revealed that the groups differed in age, with schizophrenics being significantly older than schizophreniform, unipolar depression and bipolar disorder patients, and ‘other’ psychotics being older than schizophreniform patients [F (5,108) = 5.4, p < O.OOl]. In addition, although the

number of previous admissions and age of onset of illness were found to differ between the groups (for each variable, F (5,108) = 2.4, p < 0.05) post- hoc analyses failed to reveal any significant pattern. Inspection of the means in Table 1 suggests a tendency for schizophrenics and schizoaffective disorder patients to have more admissions than the rest of the sample. Similar inspection of the means for age of onset of illness suggests a lower age of onset in schizophreniform and unipolar depressed patients in comparison to the rest of the sample. However, the differences are not great, and post-hoc contrasts failed to reveal any pattern

146

TABLE 1

Variahk Bipolar

disorder

n=23

C’nipolur

drpressiorz

n=14

Sex (m/f) 28113 4!4 712 15:8 7:7 I118

Age** 29.1 21.1 29.8 24.4 23.4 30.2

(7.6) (3.2) (8.7) (5.3) (5.4) (6.4) Onset* 26.2 21.0 27.9 23.6 22.6 27.7

(7.5) (3.1) (8.1) (5.6) (5.0) (6.4)

Education 3.7 3.2 3.4 4.3 3.7 3.3

(2.3) (2.2) (2.6) (1.8) (2.5) (1.9) Admissions* 2.5 I.1 2.4 1.5 1.5 1.3

(2.5) (0.4) (1.8) (0.9) (0.7) (0.5) Duration 51.3 64.8 38.7 55.2 56.2 42.9

(34.2) (27.8) (24.3) (34.6) (31.3) (34.6)

Prodrome** 71.6 1.8 18.0 11.7 25.9 29.6 (76.6) (3.2) (26.4) (33.2) (32.3) (38.3)

Medication 784 919 700 982 954 499

(705) (567) (510) (674) (816) (488)

Onset: Age of illness onset.

Education: Education score.

Admissions: Number of admissions.

Duration: Duration of current episode (data available for n= 108).

Prodrome: Prodrome duration in weeks (data available for II = 90).

Medication: Highest 24 h level of CPZ units (mg) in episode (data available for n= 108).

*p<o.o5; **/?<0.001

of difference. Inspection of the variables ‘Age’ and ‘Age of onset’ in Table I reveals that the sample consists of patients with recent onset of psychotic disorder. For many of the subjects this was the first psychotic episode. Prodrome duration was clearly different between the groups with a greater duration in schizophrenic subjects than in other diagnostic groups.

Statistical methods A matrix of Pearson correlations between all pos- sible pairs of symptoms (negative and positive) was generated for the whole sample. The principal method used to examine the structure of the corre- lation matrix was non-metric multidimensional scaling (MDS) (Schiffman et al., 1981; Davison, 1983). This is a graphical method which attempts to represent the correlation matrix as a map, where the correlation between each pair of symptoms is represented as a distance, so that strongly corre- lated items are close together, and weakly corre- lated items are far apart. In non-metric scaling, this distance function is not assumed to be linear.

but is derived to produce the best fit in the fewest number of dimensions. This makes it particularly suitable for the analysis of data based on ordinal measures such as rating scales. A detailed compari- son of this method with the more conventional technique of principal components analysis may be found in Davison (1985). The principal advan- tage of the MDS technique is that it can provide a good representation of a correlation matrix using fewer dimensions than factor analytic techniques. This is particularly true for many applications of factor analysis which assume that the matrix has a simple structure (discrete clusters of items). MDS can identify many other types of structure. It produces an unrotated solution which must then be interpreted by the researcher. This makes it easier to replicate findings than is the case with factor analysis, where the final solution (usually a set of loadings) is dependent on the particular methods used for factor extraction and rotation.

Prior to scaling, variables with low base rates were excluded from further analysis. The criterion for exclusion of an item was that less than 10%

147

of the sample scored 2 (mild severity but definite presence) on that item. Similar criteria have been used in other studies, e.g., Liddle (1987b). In addition, items with low communalities were iden- tified. It is important to identify such variables as

each may require anYadditional dimension to pro- duce an acceptable multidimensional scaling solu-

tion. Theoretically, items with low communalities do not share common variance with other scale items and may constitute poorly represented dimensions of pathology measured by the scale or may be highly unreliable measures of well- represented constructs. As three dimensions is usually the maximum number for ease of inter- pretation, the inclusion of such variables can make it impossible to obtain an acceptable fit. Because of the large number of variables used in the present analysis, relative to the number of subjects, the ordinary squared multiple correlation would pro- duce an inflated estimate of communality. For this reason, two adjusted correlation measures were used, i.e. adjusted R2 and a more conservative index described by Browne (1975). These are shown in Table 2 for the full set of SAPS and SANS items. Any variable with a squared multiple correlation less than 0.15 according to the conser- vative measure was excluded from the scaling analysis.

The MDS technique was augmented by hierar- chical cluster analysis using the single linkage criterion (Everitt, 1974) to produce a sorted corre- lation matrix. This can be used to check the adequacy of the scaling solution, which will rarely represent the matrix perfectly.

RESULTS

Low base rates, which would preclude meaningful measures of correlation, resulted in the exclusion of five items from any further analysis: olfactory hallucinations, delusions of jealousy, thought with- drawal, repetitive or stereotyped behavior, and clanging (all from the SAPS). The item inattentive- ness during mental status testing was excluded because 26 subjects had missing data on this item. A further eight items were excluded from the scaling analysis on the basis of low communalities (Table 2). These were: delusions of persecution,

somatic delusions, delusions of sin or guilt, aggres- sive or agitated behavior, bizarre behavior, bizarre social and sexual behavior (from the SAPS) and blocking, poor grooming and hygiene (from the SANS). The item inappropriate affect was removed from the scaling solution given that cluster analysis showed that it did not fit uniquely with any single

symptom dimension (as discussed in more detail below) despite its reasonable base rate and border- line communality value.

The remaining variables were then scaled using the ALSCAL program from the SPSSX package (SPSS Inc., 1988). A good fit was obtained in two dimensions. The adequacy of the fit in multidimen- sional scaling is a function of the correspondence between the original correlations, after the appro- priate non-linear transformation, and the distances on the map. One measure of the fit is the squared

correlation between these two sets of values (Davi- son, 1983). The two-dimensional solutions had an associated R2 value of 0.91. A three-dimensional solution did not markedly improve this value, nor did the third dimension add much structure, i.e., no variable was far from the others on the third dimension. Hence the two-dimensional solution (Fig. 1) was retained. As no technique which attempts to reduce the dimensionality of such a large matrix will ever provide a perfect fit, the matrix was also sorted using the results of the scaling analysis, augmented by cluster analysis using the single linkage criterion (Everitt, 1974). This matrix (Fig. 2) shows the first digit of the correlation. Correlations between - 0.1 and 0.1 are shown as dots, with any negative correlations of - 0.2 or higher represented by the letters shown in the key. The structure of the correlation matrix will be discussed with reference to both these figures.

General structure It is apparent from Fig. 1 that a simple positive/ negative dichotomy does not adequately represent the structure of the correlation matrix. Our inter- pretation of this MDS solution is that three broad groups of symptoms can be identified, namely Negative Symptoms, Thought Disorder, and Hallucinations/Delusions. However, the matrix, shown in Fig. 2, does not have a simple structure. Although negative symptoms cluster reasonably well, positive symptoms show a more dimensional

SAPS items

Auditory hallucinations

Voices commenting

Voices conversing

Somatic hallucinations

Visual hallucinations

Persecutory delusions

Delusions of sin or guilt

Grandoise delusions

Religious delusions

Somatic delusions

Delusions of reference

Delusions of being controlled

Delusions of mind reading

Thought broadcasting

Thought insertion

Clothing and appearance

Social and sexual behaviour

Aggressive and agitated behaviour

Derailment

Tdngentiality

Incoherence

Illogicality

Circumstantiality

Pressure of speech

Distractible speech

SA NS items

Unchanging facial expression

Decreases spontaneous movements

Paucity of expressive gestures

Poor eye contact

Affective nonresponsivity

Inappropriate affect

Lack of vocal inflection

Poverty of speech

Poverty of content of speech Blocking

Increased response latency

Poor grooming and hygiene

Impersistence at work or school

Physical anergia

Diminished recreational interests and activities Diminished sexual interest and activity

Diminished ability to feel intimacy and closeness Diminished relationships with friends and peers

Social inattentiveness

0.84 0.73 0.60 0.83 0.73 0.59 0.80 0.67 0.52 0.60 0.34 0.16 0.66 0.45 0.25 0.45 0.09 0.01* 0.48 0.15 0.03* 0.61 0.37 0.18 0.62 0.38 0.19 0.55 0.27 0.10* 0.65 0.42 0.23 0.62 0.38 0.19 0.61 0.36 0.17 0.71 0.52 0.33 0.67 0.45 0.26 0.51 0.20 0.06* 0.48 0.14 0.03* 0.56 0.28 0.1 I* 0.83 0.73 0.59 0.79 0.66 0.50 0.59 0.33 0.15

0.65 0.43 0.24 0.82 0.70 0.56 0.67 0.46 0.26 0.62 0.37 0.18

0.80 0.67 0.51

0.76 0.61 0.44 0.84 0.74 0.60 0.79 0.65 0.49

0.78 0.64 0.47

0.60 0.35 0.16**

0.80 0.67 0.51

0.78 0.64 0.48

0.70 0.51 0.32 0.52 0.22 0.07* 0.67 0.46 0.26

0.59 0.33 0.14*

0.63 0.39 0.19 0.77 0.63 0.46 0.85 0.75 0.62 0.65 0.43 0.24

0.86 0.77 0.65 0.89 0.82 0.72

0.72 0.54 0.36

*Items excluded from scaling because of low communalities. **Items excluded from scaling due to poor unique clustering

Fig. 1. Multldimcnsional scaling solution of SAPS and SANS

items for the whole sample of psychotics.

structure, being spread in a semi-circle with only a small gap between the two major groups of positive symptoms. This is also apparent in the

sorted matrix. The negative items form a block with similar correlations within that block, as to a lesser degree do the thought disorder symptoms. Hallucinations and delusions seem to fall along a continuum, as evidenced by high correlations along the diagonal of the matrix, falling away with distance from the diagonal. (Note that this reduc- tion in the correlations does not reflect changes in the base rates of the symptoms, which could also produce this type of structure.) Hence. some items at either end of this continuum, such as auditory hallucinations and grandiose delusions, are virtually uncorrelated.

Negutive s~m~ptoms

The MD.5 solution (Fig. I) indicates that there is a large group of negative symptoms which tend to co-occur, and this is also apparent in the sorted correlation matrix (Fig. 2). However. a few SANS items, including poverty of content of speech, as well as some low communality items are missing

149

from this group. Nonetheless, the validity of sepa- rating this group of symptoms from the positive symptoms is supported by the correlation matrix. However, due to the rather even correlations between these items, the subscale structure of the SANS is not readily apparent. Any separation into sub-groups (best seen in the sorted matrix due to a lack of fine-scale accuracy in the scaling solution) seems to be between items which we refer to as Negative Signs (e.g., unchanging facial expression, lack of vocal inflections, poor eye contact) and items representing Social Dysfunction (e.g., ability to feel intimacy and closeness, diminished recrea- tional interests and activities, loss of sexual interest and activity). Although there is such separation, these two sub-groups are clearly correlated.

Thought disorder

This group of symptoms clearly forms a separate cluster of symptoms, a finding which supports the structure of the original scale. Poverty of content of speech, a SANS item, appears to be more closely related to Thought Disorder items than to other SANS items. Some individual thought disorder symptoms, notably pressure of speech, display moderate negative correlations with the negative symptom group. Overall there seems to be a slight negative correlation between these two groups as a whole.

Hallucinations and delusions

As in the Negative Symptoms, there is additional structure within the Hallucinations/Delusions group, although there is an absence of tight clus- ters. These symptoms appear to be arranged along a continuum. Although hallucinations are situated at one end, there is no clear break between them and the delusions, particularly in the full matrix where somatic delusions bridge the gap (Fig. 2). Within the delusions items some further separation may be discerned. The first sub-group (consisting of grandiose delusions, delusions of reference and religious delusions) we have referred to as ‘Grandi- osity’ and the second sub-group (consisting of thought broadcasting, delusions of mind reading, thought insertion and delusions of control) we have referred to as delusional symptoms represent- ing ‘Loss of Boundary’. This division, although empirically somewhat arbitrary, may be useful as

(hallucinations)

(hallucinations)

VISUAL

HALLUCINATIONS

(22)

DELUSIONS

OF MIND READING

(37)

43444.5

3.342.44

THOUGHT

INSERTION

(33)

2.233.535

idelusionsj

1

AA......

(thought

disorder)

(thought

disorder)

(thought

disorder)

(thought

disorder)

TSOUGBT

(thought

disorder)

DISORDER

(thought

disorder)

(thought

disorder)

1

(affective

flattening)

-

(affective

flattening)

(affective

flattening)

(affective

flattening)

;a:i;czve

flattening)

(aaffective flattening)

(alogia)

(avolition)

(attention)

-

2.........AAAAAS.C...454465546

3

diminished

recreational

interests

(54)

(anhedonia)

Z.......A.AAA....S...4544545342

I

2 .....

A.A

.AA

AA

A..S

..2~i

~~:::

iij~~

“ed

int~

=c~’

65’

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$j

dimuushed

relatlonshlps

(60)

222.2..2.........A

...

impersiatence

work/school

(67)

...............

..S

...

diminished

sexual

interest

(48)

.*.2.

3,..2.....A.......A

;;.....::::.

......

PERSECUTORY

DELUSIONS

(64)

A.....2..23.32.2.2..2

....

DE

LU

SIO

NS

O

F GUILT/SIN

(27)

.A

..

22.2

.2

.. 22.2.2.22......2

..........

A'.%RESSION/AGITATION

(28)

........

..2.2....2

.....................

CLOTSING

h APPEARANCE

(18)

SO

CIA

L

DY

S-

- F

UN

CT

’ION

S

(delusions)

(delusions)

(bizarre)

(bizarre)

NEGATIVE

SYMPTCJNS

.A

. .

. .

. .

. ..L

I....Z

.L...

......

.2...

.....4

SOCIAL

6 SEXUAL

BESAVIOR

(22,

2......3......22..2..3222232242.A.3.

(bizarre)

ii;;:.

diminished

grooming

& hygiene

(35)

222....

(avolition)

2..2A3..222.22.4232..2.,3A..2

blocking

(47)

. . . . . . . . . . . ..32.22433.....23..3.......2..22

(alogia)

inappropriate

effect

(36)

(affective

flattening)

. denotes

correlations

-.l to .l

A denotes

correlations

-.2

B denotes

correlations

-.3

C denotes

correlations

-.4

Fig, 2, sorted matrix of Correlations between

a11 Common

(>

10%

) items.

Sym

pto

m

ba

se r

ate

s a

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ho

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a

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mp

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pe

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b

rac

kets

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151

a way of representing this very broad group.

Persecutory delusions

the range of symptoms in

This symptom is dealt with separately because it is the only low communality item with a high base rate. The observation that persecutory delusions occurs independently of other delusions (apart from a weak correlation with delusions of refer- ence) suggests that its inclusion in the delusions sub-scale of the SAPS may be inappropriate.

Low communality symptoms and inqpropriute

qfect

There are several items which are not tightly correlated with each other or with any group. This, combined with fairly low base rates in many cases, makes it difficult to draw definite conclusions about where these symptoms might belong. Items from the bizarre behavior sub-scale of the SAPS do not form a coherent group and are not consis- tently correlated with other symptoms in the SAPS or the SANS. Inappropriate affect correlates most consistently with Thought Disorder items (especi- ally tangentiality, distractible speech, incoherence, and poverty of content of speech), but it also correlates with Negative Symptoms items such as social inattentiveness and lack of eye contact. Blocking correlated with a number of items from the positive group (auditory hallucinations, voices commenting, distractible speech, delusions of guilt or sin) and from the negative group (prolonged speech responsiveness, social inattentiveness). It would seem, therefore, that inappropriate affect and blocking have ambiguous status in relation to the positive and negative symptom classification. The item social inattentiveness, although more highly correlated with Negative Symptoms items, is also consistently correlated with Thought Disor- der items. Uncertainty about where these items fit, combined with low base rates in some cases, limits their usefulness in calculating summary scores or making global judgements at the sub-scale level.

The structure in schkophreniu

A question which arises is whether the dimensional structure among symptoms is stable across diag- nosis. To explore this issue the results for schizo- phrenic and non-schizophrenic sub-samples were re-analysed separately. These results should be

interpreted with caution given the reductions in the respective sample sizes. Fig. 3 summarises these analyses (the variables are labelled accor- ding to Fig. 1). R* values for these two solutions were 0.84 (for schizophrenics) and 0.90 (for non-

schizophrenics) suggesting a reasonable rep- resentation of the respective item inter-correlation

matrices. It is clear from Fig. 3 that the general three dimensional structure holds for both the schizophrenic and non-schizophrenic groups with Negative Symptoms, Thought Disorder, and Hal- lucinations/Delusions being clearly separated. Some instability in the structure is observed only within these symptom clusters. For schizophrenics, for example, the separation between Social Dys- functions and Negative Signs is less clear than that observed in the remaining psychotics group. The items within the Thought Disorder cluster, across the two sub-samples, show only minor positional variations. The distribution of items within the

Schzophrenics (n = 41)

l PCS

D/S.

ILL 0

Non-Schizophrenics (n = 73)

Fig. 3. Multidimensional scaling solutions of SAPS and SANS

items for schizophrenics and non-schizophrenic psychotics.

152

Hallucinations/Delusions dimension was found to be fairly similar for the two sub-samples, with

Grandiosity items appearing at one end of the continuum (towards Thought Disorder), Halluci- nations at the other, and Loss of Boundary Delu- sions in the middle. Compared to the schizophrenic group, Grandiosity items in the non-schizophrenic psychotics tended to be closer to the Thought Disorder cluster of items. For the schizophrenic group somatic hallucinations tended to be more strongly correlated with Loss of Boundary Delu- sions, though there was a similar trend for the non-schizophrenic sub-sample. It should be remembered that sample size reductions may have contributed to the other minor variations in the

positioning of items between sub-samples.

DISCUSSION

In this study an item-level analysis was conducted of the SAPS and SANS using exploratory rather than confirmatory techniques in the search for structure. The results suggest three major, indepen- dent groups of symptoms, with additional structure within two of these groups. This finding is in broad agreement with previous research which has iden-

tified the negative group as independent from hallucinations/delusions and from thought disor- der (Bilder et al., 1985; Kulhara et al., 1986; Liddle, 1987b; Simpson and Davis, 1985; Arndt et al., 199 1). Despite the fact that these studies employed different scales to measure psychiatric symptoms. and different clinical samples, there is a consider- able similarity between their findings and the find- ings reported here.

The present findings demonstrate that within the broad class of positive symptoms there are at least two independent groups. Thought Disorder forms a coherent group which is independent of both the Negative Symptoms and Hallucinations/ Delusions. Hallucinations/Delusions can be fur- ther subdivided, although precisely where the boundary should be drawn is uncertain. At one end of this group are‘ auditory, visual and somatic hallucinations. and at the other grandiose delu- sions, delusions of reference and religious delu- sions, a group we have referred to as ‘Grandiosity’. Bridging the gap between these two groups is a

group of delusional symptoms representing what we have referred to as ‘Loss of Boundary’- delusions of mind reading. thought insertion. thought broadcasting and delusions of control. These appear to be similarly related to the group of Hallucinations and to the Grandiosity group of delusions. Our results regarding the positive group of symptoms, although not identical, are very similar to those reported by other authors (Bilder et al., 1985; Simpson and Davis, 1985; Kulhara et al., 1986; Liddle, 1987b; Arndt et al., 1991) except that our use of the full scales reveals considerable heterogeneity within hallucinations and delusions.

A further departure from previous findings con- cerns the status of persecutory delusions which varied independently of other delusions (apart from delusions of reference), hallucinations and thought disorder. This finding is consistent with the report by Kay and Sevy (I 990) of work con- ducted using the Positive and Negative Symptom Scale (PANSS). Using principal components analy- sis of data gathered from a sample of 240 schizo- phrenics seven components were extracted. Of particular interest in the context of the present discussion is that the PANSS item suspicious/ persecution loaded on a separate factor from other positive symptoms. This factor also had loadings from items of hostility, active social avoidance and uncooperativeness~commonly considered in scales measuring paranoia (Lorr, 1964; Magaro et al., 1981; Bigelow and Berthot, 1989) or evident in subtypes of psychotics (McNair et al., 1964). Given the qualitatively distinct nature of persecu- tory delusions, and their independent occurrence in disorders such as delusional disorder, it may be worth exploring whether it ought to be treated separately as a fourth major dimension of psychotic illness similar to those identified pre- viously (Wittenborn and Holzberg, 1951; Lorr et al., 1955; Lorr and O’Connor, 1962).

In addition to this, the present item level analysis shows that considerable redundancy exists amongst some of the remaining positive symptoms. For example. there are three items dealing with auditory hallucinations, and many of the thought disorder symptoms are highly correlated and prac- tically similar. This may or may not be desirable, depending on the nature and purpose of the scale. If it could be shown that all symptoms do fall into

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discrete. independent groups then it may be useful to have a number of items which tap the same underlying construct with little unique variance, in order to improve measurement accuracy. However, the current findings show the positive symptoms to be spread on a continuum with little natural clustering, apart from that due to including items such as those mentioned above which are very similar. In that case it may be better to select items which are more evenly spaced so that the scale is not biased towards any particular region of the continuum. For coarse-level measurement we would suggest, on the basis of the present findings, that the positive symptoms be subdivided into Thought Disorder, Hallucinations, ‘Loss of Boundary’ Delusions, Grandiose Delusions and Persecutory Delusions.

The items of the SANS clearly form a more coherent scale than do those of the SAPS but there is little evidence for the sub-scale structure of the SANS. We would suggest that a useful distinction may be made between those SANS items we have referred to as Negative Signs and items represent- ing symptoms of Social Dysfunction, although these two sub-groups are clearly correlated. The first group consists predominantly of items from the affective flattening sub-scale, with an additional two items from the alogia sub-scale, and the second group consists predominantly of items from the anhedonia sub-scale, with an additional two items from the avolition sub-scale. Between these two sub-groups of negative items lie the items physical anergia and social inattentiveness (the latter is scored during the mental status examination). These two items appear to tap both the constructs of Negative Signs and Social Dysfunctions. In addition, the item social inattentiveness is also related to Thought Disorder items consistent with previous work (Bilder et al., 198.5; Liddle, 1987b).

The above results suggest that, in the search for relationships between psychotic psychopathology and external correlates of psychopathology (e.g., brain structure, cognitive functioning, neuro- endocrine measures and so on), and in attempts to identify phenomenological predictors of course and outcome, use of the SAPS total item (or composite) score or the sum of global scores as summary measures may be misleading. It may also be inappropriate to use the delusions sub-scale score or global score for this purpose, given our

finding that delusions of persecution vary indepen- dently from all other delusions (with the exception of delusions of reference) and the ‘Loss of Bound- ary’ delusions are similarly correlated with halluci- nations as with other delusions.

A further issue highlighted by the present analy- ses is that the content of the SAPS is not well balanced with respect to either the number of items used to measure a particular construct, nor with regard to the sensitivity or frequency of occurrence (or base rates) of the items. This is less of a problem in the case of the SANS. Andreasen (1987) in a sample of schizophrenic patients, reported base rates below 20% (taking scores > 2) for 16 of the 30 items of the SAPS. In our sub- sample of schizophrenic patients (n = 41) 15 of the 30 items had base rates less than 20%, 11 of these being the same items reported by Andreasen (I 987) to have low base rates. In Andreasen’s sample, the only SANS item with a base rate less than 20% was blocking whereas in our schizophrenic sub- sample no SANS item had a base rate less than 20%. In the absence of larger samples it is difficult to say where some of the SAPS items fit in the dimensional structure.

The use of the total SANS score (or sum of globals) for the purpose of data reduction would appear, from the present analyses, to be more justified than a similar procedure with the SAPS,

although poverty of content of speech and inappro- priate affect appear to be more closely related to Thought Disorder than to Negative Symptoms. Mortimer et al. (1989) constructed a new scale for the assessment of negative symptoms which did not include these items. Inappropriate affect was excluded from the scale as it did not correlate with other negative symptoms (see also, Andreasen, 1982; Andreasen and Grove, 1986). Poverty of content of speech was excluded on the basis of poor inter-rater reliability. Liddle (1987b) found that this item was commonly loaded with other items measuring thought disorder, a finding consis- tent with the present results. In the present study, blocking, despite its reasonable base rate, was found to be relatively non-specific to negative symptoms while other studies have found low inter-rater reliability and poor relationship to other negative symptoms for this item (Andreasen and Grove, 1986).

Another important issue concerns the relation-

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ship between positive and negative symptoms. Andreasen and Olsen (1982) found that negative symptoms and hallucinations/delusions loaded on a single bipolar factor, with negative symptoms and hallucinations/delusions being negatively correlated. The present results, contradict this finding, as do the results of other studies (Bilder et al., 1985; Simpson and Davis, 1985; Kulhara et al., 1986; Liddle, 1987b; Arndt et al., 1991).

Kay et al. (1987) also held the view that positive and negative symptoms ‘represent opposing polari- ties of psychopathology’ (p. 79, Kay and Opler, 1987) since their analysis revealed a negative corre- lation between these two groups of symptoms. However, this inverse relationship was found only when scores from their General Psychopathology scale were partialled out. This may have been an inadequate analytical strategy in the first place since subsequent analysis (Kay and Sevy, 1990) revealed that items from their General Psychopa- thology sub-scale tended to be distributed among the positive, negative and other psychopathology dimensions. Furthermore, Lenzenweger et al.‘s (1989) direct test of the bipolar model through confirmatory statistical methods failed to support

the model. The present findings suggest that a more subtle

bipolarity between positive and negative symptoms may exist in that Negative Symptoms items tended to be inversely correlated with Thought Disorder items, and especially, pressure of speech. and partly with Grandiosity items. This suggests that negative symptoms may be at opposing poles of psychopa- thology to symptoms surrounding the construct of activation or excitation, which is a poorly repre- sented dimension in the Andreasen scales. This would be consistent with older work on the devel- opment of other scales measuring activation;‘exci- tation and withdrawal which have empirically found (Lorr et al., 195.5, 1962) or treated (Venables, 1957) the two symptom complexes as polar oppo- sites. Lenzenweger et al. (1989) did not support the present view of bipolarity, however, they did not test a model with more than two dimensions, and indeed their best two dimensional model was an inadequate description of the relationships among the symptoms (Arndt et al., 1991).

There is now sufficient evidence in the literature to conclude that the positive*egative symptom dichotomy is an over-simplification and can be

misleading, particularly when summary measures of ‘positive symptoms’ and of ‘negative symptoms’ are used. It may be that the terms positive and negative symptoms need to be dropped in recogni- tion of the greater complexity of the situation. particularly in the case of positive symptoms. The present study suggests perhaps four dimensions are needed to account for specifically psychotic symptoms, excluding any consideration of mood disturbances. Kay and Sevy’s (1990) analysis of the PANSS yielded factors corresponding to hallu- cinations,idelusions, thought disorder and suspi-

cious/persecution as well as negative symptoms, excitement and depression. However. they regarded their thought disorder and persecution factors as unreliable. partly due to the low propor- tion of variance explained by these dimensions. Since this may reflect the smaller number of symp- toms tapping these factors, we suggest that this exclusion is premature, and that six dimensions rather than four may be required for a fuller account of psychotic and mood symptoms. This conclusion is supported by work carried out before the rise to popularity of the positive/negative distinction (e.g.. Wittenborn, 1951; Lorr et al..

1955: Overall and Woodward. 1975). The present study adopted a strategy of includ-

ing a diagnostically heterogeneous sample of psychotic patients. This strategy can be expected to yield the maximum number of independent dimensions of psychosis. Further work using this strategy should aim for larger and more equivalent sub-sample sizes with respect to diagnostic groups. This should yield a more accurate and balanced picture of the relationships between symptoms and lead to the development of a more comprehensive instrument to measure psychotic symptoms and signs. A second or concurrent strategy is to analyse the dimensionality peculiar to specific subgroups of patients including, samples of drug-free patients, patients at different phases of illness, patients with different diagnoses and in groups from different cultural backgrounds. It would then be possible to assess the stability and generalizability of the structure reported here. In the present study cross- diagnostic generality was explored tentatively by re-analysing results for the sub-sample of schizo- phrenic patients and comparing these to similar results for the remaining psychotic sub-sample. It was found that the essential elements of the struc-

155

ture remained stable across these two groups. However, these results should be treated with caution due to the small sample sizes and possible distortion of the correlations among items resulting from this.

In the future it would be useful to extend the psychometric evaluation of the items of the SAPS and SANS or other instruments to include the thresholds or sensitivities of different items, and the effects on reliability of rating symptom severity vs presence/absence. However, this would require larger samples than those used by Andreasen and Olsen (I 982), Andreasen and Grove (1986) or ourselves. In addition, there ought to be further development of the scales to include dimensions which we have suggested are poorly measured currently. It is also necessary to test the major symptom sub-groups’ criterion and predictive validity by investigating organic, cognitive, social functioning, treatment response and clinical outcome measures. Such investigations of criterion and predictive validity of these symptom sub-gro- ups should no longer be limited to schizophrenia, but should include examination of all the major psychotic disorders, since the boundaries of the various psychotic disorders continue to be unclear.

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