Department of Psychiatry, University of British Columbia, Canada
Ealing Hospital, London
Graylingwell Hospital, Sussex, UK
Correspondence: Professor Peter F. Liddle, Division of Psychiatry, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK. E-mail: peter.liddle{at}nottingham.ac.uk
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aims To test the reliability, sensitivity to change and factor structure of a new scale for the assessment of the Signs and Symptoms of Psychotic Illness (the SSPI).
Method Interrater reliability was evaluated by determining the intraclass correlation for the ratings of 63 patients. Sensitivity to change was assessed in a longitudinal study of 33 patients. Factor structure was determined from scores for 155 patients.
Results The intraclass correlation was satisfactory for all individual items and excellent for the total score. Scores were sensitive to change. A change in Clinical Global Impression of one unit corresponded to an SSPI total score change of 31%. Factor analysis revealed five clusters of symptoms.
Conclusions The SSPI provides a sensitive and reliable measure of the five major clusters of symptoms that occur commonly in psychotic illness.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We describe an investigation of interrater reliability, factor structure and sensitivity to change of a new scale for the assessment of the Signs and Symptoms of Psychotic Illness (the SSPI).
![]() |
Existing instruments for assessing psychotic symptoms |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Furthermore, in both PANSS and BPRS a single phenomenon might contribute to the score for more than one item. For example, in the PANSS item suspiciousness, the highest score denotes beliefs of delusional intensity. A persecutory delusion might contribute strongly to PANSS scores for suspiciousness, delusions and unusual thought content. Similarly, a grandiose delusion might contribute to scores for grandiosity, delusions and unusual thought content, whereas a delusion of guilt might contribute to scores for guilt feelings, delusions and unusual thought content. As a consequence, alleviation of a persecutory, grandiose or guilty delusion might have a greater impact on the global score than the alleviation of some other psychotic symptom.
![]() |
The Signs and Symptoms of Psychotic Illness scale |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
To avoid the problem of some specific types of delusion contributing to the score for several different items, and thereby making a disproportionate contribution to global score, the SSPI has a single item for severity of delusions that contributes to the score for global severity. In addition, there is an optional delusion sub-scale, including items for specific types of delusions (guilty, grandiose, paranoic, Schneiderian) and for the mood incongruence of delusions. In situations in which the specific content of delusions is of interest, such as for the purpose of diagnosis or for measuring response to a treatment that might be expected to have a different effect on different types of delusions, the sub-scale item scores can be used. Similarly, a single score for severity of hallucinations contributes to the score for global severity, but there is a separate optional hallucination sub-scale that contains items for second person auditory hallucinations, Schneiderian hallucinations and mood incongruence of hallucinations.
Item content is defined in a glossary (available on request from the author) and item scores are assigned according to specified guidelines, on the basis of observed behaviour at interview and responses to questions regarding symptoms and behaviour during the past week. The interview is semi-standardised. There are 15 specified direct questions about symptoms and whenever these questions elicit evidence of psychopathology the interviewer asks further questions to establish the nature and severity of the phenomena. In addition, the interviewer conducts an inquiry into occupational activities, social function and the patient's understanding of the illness and its treatment. A brief test of attention and orientation is administered. The interview typically lasts 25 min. If there is reason for concern regarding the reliability of the patient's report of behaviour, a nurse or relative should be asked about level of activity and evidence of hostile or peculiar behaviour.
Severity of each item is rated in the range 0-4 (1, experiences or behaviour that are of questionable abnormality; 2, phenomena that are definitely abnormal but mild; 3, pathology of moderate severity that has a substantial impact on mental functioning; 4, severe psychopathology).
![]() |
METHOD |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Interrater reliability
Interrater reliability was determined in two studies. Two novice raters
participated in the first study: two trainee psychiatrists (K.K. and G.D.),
each with 3 years of psychiatric clinical training, underwent an SSPI training
programme that entailed the scoring of five video-recorded SSPI interviews and
comparing their scores with those assigned by the senior investigator (P.F.L.)
who had designed the scale. After completion of this training, K.K. and G.D.
interviewed 32 patients. For each interview, one of the trainees acted as the
interviewer while the other was a silent observer. At completion of the
interview they each assigned SSPI scores without conferring. In the second
study, K.K., G.D. and P.F.L. each scored video-recorded interviews of 20
patients. The intraclass correlations between the ratings by the three
investigators were computed.
Factor analysis
To determine the factor structure of SSPI scores, factor analysis was
performed on the scores for the 19 SSPI items (excluding insight) assigned at
the initial interview of each of the 155 participating patients. Insight was
excluded from the factor analysis because it was assessed in part on the basis
of the patients' beliefs regarding their symptoms. Principal components with
eigenvalues greater than unity were extracted, and these components were
subjected to oblique rotation using the Promax procedure, employing SPSS for
Windows, release 10.0.5 (1999). Scores for each subject for each factor were
assigned by summing the item scores for all items with a loading greater than
0.6 in that factor. This simple procedure was adopted because a sum of
relevant item scores can be compared readily between patients from different
samples. Analysis of variance was employed to compare the factor scores in
different diagnostic groups.
Sensitivity to change
To determine the sensitivity of SSPI scores to change in clinical state,
longitudinal assessments were performed in 33 acutely ill patients. The SSPI
scores were assigned shortly after admission to hospital and again either when
the patient was judged fit for discharge from hospital or after a maximum of 6
weeks. In 22 of these cases, the overall severity of illness was assessed
using the severity score of the Clinical Global Impression (CGI) scale
(Guy, 1976) by the patient's
attending physician on the day of each SSPI assessment. The correlation
between change in SSPI global score and change in CGI severity score was
computed.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Interrater reliability
There were no significant differences between intraclass correlation
coefficients (ICCs) for any of the three possible pairs of raters, nor between
the two studies. Therefore, the overall ICC values for each item and for the
SSPI total score derived from both studies (63 subjects in total: 43 assessed
by two raters and 20 assessed by three raters) were computed according to the
procedure described by Bartko & Carpenter
(1976), as shown in
Table 1. All coefficients for
individual items indicate acceptable interrater reliability (ICC>0.68). For
more than half of the individual items and for the SSPI total score,
interrater reliability was excellent (ICC>0.80).
Factor structure
Principal component analysis revealed five principal components with
eigenvalues exceeding unity. After rotation, five readily interpretable
factors were obtained (Table
2). Underactivity, flat affect, poverty of speech and anhedonia
loaded heavily in the first factor. This factor reflects the core negative
symptoms similar to the symptom cluster previously designated as psychomotor
poverty by Liddle (1987).
Overactivity, insomnia, elation and pressure of speech loaded heavily in the
second factor. This factor reflects psychomotor excitation. Hostility also
exhibited a substantial loading in this factor. Inappropriate affect, formal
thought disorder and attentional impairment loaded heavily in the third
factor. These are features previously identified as components of the
disorganisation syndrome (Liddle,
1987). Anxiety and depression loaded heavily in the fourth factor.
In the fifth factor, delusions and hallucinations had loadings greater than
0.6, whereas somatic concern exhibited a modest loading. This fifth factor is
similar to the reality distortion factor identified by Liddle
(1987).
|
The five rotated factors were almost orthogonal. The only correlations between factors that exceeded 0.2 were a negative correlation of -0.21 between the psychomotor poverty and excitation factors and a positive correlation of 0.26 between the excitation and disorganisation factors.
Figure 1 shows the profile of factor scores for the four main diagnostic groups (acute schizophrenia; persistent schizophrenia; schizoaffective disorder; mania) included in the study. It can be seen that all five clusters of symptoms occur in all four diagnostic groups, although the mean severity of psychomotor poverty in mania is very low and is accounted for mainly by mild flattening of affect, which might be due to the effects of antipsychotic medication in a few cases. Analysis of variance indicated significant differences between the four diagnostic groups in severity of psychomotor poverty (F(3,146)=5.1, P=0.002), reality distortion (F(3,146)=3.1, P=0.03) and excitation (F(3,146)=28.3, P<0.001). The group differences in disorganisation (F(3,146)=0.32, P=0.81) and anxiety/depression (F(3,146)=0.62, P=0.6) were not significant. The differences between diagnostic groups were due largely to anticipated differences between patients with schizophrenia and patients with mania. Planned comparisons revealed that patients with mania had significantly less severe psychomotor poverty but more severe excitation than patients with either acute schizophrenia or persistent schizophrenia (P<0.005 for all comparisons). Furthermore, patients with mania had significantly less severe reality distortion than patients with acute schizophrenia (P=0.008) or persistent schizophrenia (P=0.006).
|
Sensitivity to change
The 33 acutely ill patients participating in the longitudinal study
included 22 with schizophrenia, 4 with schizoaffective disorder, 5 with
bipolar disorder (manic phase) and 2 with other psychoses. Their mean age was
27.3 years (range 18-44 years) and the mean duration of illness was 4.5 years
(range 0.2-23 years). There were 19 male patients. The mean duration between
first and second assessments was 4.7 weeks (range 4-6 weeks). At the first
assessment the mean global SSPI score was 19.5 (s.d.=8.3) and at the second
assessment the mean global score was 9.2 (s.d.=5.9). The mean percentage
reduction was 49.2% (s.d.=27.7). In the subset of 22 patients with CGI scores,
the mean reduction in CGI score was 1.45 and the correlation between reduction
in global SSPI score and CGI score was 0.67 (d.f.=21, P=0.001,
two-tailed).
Of those patients with schizophrenia or schizoaffective disorder, the mean initial total SSPI score was 18.4 (s.d.=6.5), the mean reduction of SSPI score was 9.5 (s.d.=7.0) and the mean percentage change in SSPI was 48.7% (s.d.=27.4). The mean baseline CGI score was 4.3 (s.d.=0.96) and the mean reduction in CGI score was 1.55 (s.d.=1.04). Thus, assuming that the CGI provides a linear estimate of illness severity over the middle part of its range, a reduction of one point in the CGI score corresponds to a reduction of 6.1 units (or 31%) in the global SSPI score for those patients with schizophrenia or schizoaffective disorder.
The severity of all individual SSPI symptom items decreased from first to second assessment. However, for underactivity, flat affect, poverty of speech, somatisation and disorientation this reduction was not statistically significant. For anxiety, depression, anhedonia, attentional impairment, overactivity, pressure of speech, hostility, peculiar behaviour and impaired insight the reduction achieved a moderate level of significance (2.0<t<3.56; d.f.=32; P<0.05). For elation, insomnia, delusions, hallucinations, formal thought disorder and inappropriate affect the reduction was highly significant (t>3.56; d.f.=32; P<0.001).
Similarly, all factor scores decreased from the first to the second assessment (see Fig. 2). However, the decrease in psychomotor poverty exhibited only a trend towards statistical significance (t=1.96, P=0.058). The reduction in anxiety/depression was of moderate significance (t=2.6, P=0.013) but there were highly significant reductions in reality distortion (t=5.8, P<0.001), disorganisation (t=5.6, P<0.001) and excitation (t=4.2, P<0.001).
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Factor structure
The relationships between items, as revealed by factor analysis, reflect
the clustering of symptoms predicted on the basis of recent studies (e.g.
van Os et al, 1996;
Wickham et al, 2001).
The factor that accounted for the most variance was that representing
psychomotor poverty, reflecting the uniformly high correlations between the
core negative symptoms that loaded strongly on this factor. The second factor
representing psychomotor excitation accounted for a similar fraction of the
variance. The third factor, disorganisation, reflected the moderately strong
mutual correlations between formal thought disorder, inappropriate affect and
attentional impairment. The fourth factor, anxiety/depression, reflected the
moderately strong correlation between anxiety and depression (Pearson
coefficient r=0.57, n=155, P<0.001). The factor
accounting for the least variance was reality distortion, reflecting the fact
that the correlation between the two cardinal components of this cluster
delusions and hallucinations was of only modest strength but
highly significant (Pearson coefficient r=0.35, n=155,
P<0.001).
The factor structure of the SSPI is similar to the factor structure delineated by several studies of the PANSS (Kay & Sevy, 1990; Lindenmayer et al, 1995; White et al, 1997). The most notable difference between the symptom factor structure of the SSPI and the PANSS is that the SSPI yields a disorganisation factor comprising inappropriate affect, formal thought disorder and attentional impairment, whereas the corresponding factor in analyses of PANSS items (labelled cognitive disorganisation) usually loads most heavily on impaired abstract thinking. However, the items loading on this PANSS factor are inconsistent between studies. One large study, of 1233 patients, did not identify a cognitive disorganisation factor at all, despite confirming the composition of the other four symptom clusters (White et al, 1997). This inconsistency might be expected from the fact that several individual PANSS items embrace disorganised and impoverished mental activity within the one item. On the other hand, in the SSPI, PSE and CASH there is minimal confounding of phenomena reflecting disorganisation and impoverishment of mental activity within items. The symptoms loading on the disorganisation factor identified by analysis of SSPI items resemble those obtained from analysis of PSE items (Liddle, 1987) and from analyses of CASH items (Liddle, 1987; Klimidis et al, 1993).
Although the factor composition closely reflects that predicted on the basis of recent studies, several unpredicted features are worthy of note. First, anhedonia loaded mainly on the psychomotor poverty factor and minimally on the anxiety/depression factor. The association between anhedonia and other psychomotor poverty symptoms might reflect, at least in part, the possibility that psychomotor poverty symptoms can be secondary to depression. It is probable that in a sample of patients with psychotic depression a stronger association between depression and anhedonia would be observed. Similarly, somatic concern exhibited a moderate loading on the reality distortion factor and a small loading on the anxiety/depression factor. Again, it is possible that a stronger association between anxiety/depression and somatic concern would be observed in a sample of patients with psychotic depression. However, somatic concern is moderately common in schizophrenia. A score of 2 or more was recorded in 26% of all patients with schizophrenia. Scrutiny of the video-recorded interviews indicated that the somatic concern was not considered to be of delusional intensity in any of these cases. None the less, the association between somatic concern and reality distortion suggests that the pathological process responsible for somatic concern in psychotic illnesses might share features in common with that responsible for delusions.
Sensitivity
The SSPI global score exhibited a substantial reduction from the initial to
final assessment in the patients assessed longitudinally. This is likely to be
due, at least in part, to the inclusion of five patients with mania and four
with schizoaffective disorder in the sample. It is potentially informative to
examine the relationship between change in global symptom severity assessed
using the BPRS or PANSS, and change in global severity of illness measured
with CGI, in published treatment trials. In a meta-analysis
(Tandon et al, 1997)
of treatment trials comparing the antipsychotic ziprasidone with placebo in
patients with schizophrenia and schizoaffective disorder (with baseline mean
CGI score of 4.8), the reduction in CGI after 4-6 weeks in the patients
treated with ziprasidone was 0.54. The mean reduction in BPRS score was 13%
and the mean reduction in PANSS score was 14%. Thus, for both BPRS and PANSS a
reduction of approximately 25% in the global symptom score corresponds to a
one-point decrease in CGI score (assuming a linear relationship in the middle
of the CGI range). Because of the differences in patient samples, comparisons
between studies should be interpreted with caution. None the less, the finding
that in the patients with schizophrenia and schizoaffective disorder in this
study a reduction of 1 unit in the CGI score corresponded to a 31% reduction
in SSPI global score indicates that the sensitivity of the SSPI global score
to change in illness severity is at least as high as that of the BPRS and the
PANSS.
![]() |
Clinical Implications and Limitations |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LIMITATIONS
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Andreasen, N. C. (1986) Comprehensive Symptoms and History. Iowa City, IA: University of Iowa.
Bartko, J. J. & Carpenter, W. J. (1976) On the methods and theory of reliability. Journal of Nervous and Mental Disease, 163, 307-317.[Medline]
Guy, W. (1976) ECDEU Assessment Manual for Psychopharmacology. Revised DHEW Pub. (ADM). Rockville, MD: National Institute for Mental Health.
Johnstone, E. C., Crow, T. J. & Frith, C. D. (1978) Mechanism of the antipsychotic effect in the treatment of acute schizophrenia. Lancet, ii, 848-851.
Kay, S. R. (1991) Positive and Negative Syndromes in Schizophrenia. New York: Brunner Mazel.
Kay, S. R. & Sevy, S. (1990) Pyramidical model of schizophrenia. Schizophrenia Bulletin, 16, 537-545.[Medline]
Klimidis, S., Stuart, G. W., Minas, I. H., et al (1993) Positive and negative symptoms in the psychoses: reanalysis of published SAPS and SANS global ratings. Schizophrenia Research, 9, 11-18.[CrossRef][Medline]
Liddle, P. F. (1987) The symptoms of chronic schizophrenia. A re-examination of the positivenegative dichotomy. British Journal of Psychiatry, 151, 145-151.[Abstract]
Liddle, P. F., Carpenter, W. T. & Crow, T. (1994) Syndromes of schizophrenia. Classic literature. British Journal of Psychiatry, 165, 721-727.[Medline]
Lindenmayer, J. P., Bernstein-Hyman, R., Grochowski, S., et al (1995) Psychopathology of schizophrenia: initial validation of a 5-factor model. Psychopathology, 28, 22-31.[Medline]
Overall, J. E. & Gorham, D. R. (1962) The brief psychiatric rating scale. Psychological Reports, 10, 799-812.
Tandon, R., Harrigan, E. & Zorn, S. H. (1997) Ziprasidone: a novel antipsychotic with unique pharmacology and therapeutic potential. Journal of Serotonin Research, 4, 159-177.
van Os, J., Fahy, T. A., Jones, P., et al (1996) Psychopathological syndromes in the functional psychoses: association with course and outcome. Psychological Medicine, 26, 161-176.[Medline]
White, L., Harvey, P. D., Opler, L., et al (1997) Empirical assessment of the factorial structure of clinical symptoms in schizophrenia. A multisite, multimodel evaluation of the factorial structure of the Positive and Negative Syndrome Scale. The PANSS Study Group. Psychopathology, 30, 263-274.[Medline]
Wickham, H., Walsh, C., Asherson, P., et al (2001) Familiarity of symptom dimensions in schizophrenia. Schizophrenia Research, 47, 215-222.[CrossRef][Medline]
Wing, J. K., Cooper, J. E. & Sartorius, N. (1974) The Description and Classification of Psychiatric Symptoms: an Instruction Manual for the PSE and CATEGO System. London: Cambridge University Press.
Received for publication January 28, 2001. Revision received August 14, 2001. Accepted for publication August 14, 2001.
Related articles in BJP: