Experience of Negative Symptoms: Comparison of Schizophrenic Patients to Patients With a Depressive Disorder and to Normal Subjects

Many reports have indicated that unawareness of illness is a prevalent feature of schizophrenia and plays an important role in its course and treatment. In addition, unawareness has been shown to be modality-specific: patients may be aware of some, but not all, signs of the disorder (1–4). In order to examine the experience of negative symptoms, we developed a self-rating scale: the Subjective Experience of Negative Symptoms (5). Since the 21 items of the scale were taken from the Scale for the Assessment of Negative Symptoms (SANS) (6), the patient's rating can be compared to the psychiatrist's rating for the corresponding SANS item. In addition to awareness of negative symptoms, the Subjective Experience of Negative Symptoms scale attempts to obtain information on the patient's attributions for negative symptoms and to measure the level of distress ascribed to such symptoms. The reliability of the scale has been proved to be sufficient (5).

When we compared schizophrenic patients' self-ratings to ratings made by a psychiatrist, the results (manuscript by J.P. Selten et al. submitted for publication) agreed with those of previous studies (3, 4): the patients underestimated the frequency and severity of negative symptoms, and few patients attributed negative symptoms to mental illness. Furthermore, when the patients were asked whether these symptoms were a source of disruption or distress, their replies were more often negative than affirmative. We expected that these results would become more meaningful when examined against a point of comparison. For that reason we administered the Subjective Experience of Negative Symptoms scale to patients with a depressive disorder and to normal subjects. It is important to note that depressed patients display impairments that are phenomenologically very similar to negative symptoms in schizophrenia. Affective flattening, poverty of speech, lack of drive or energy, and social withdrawal are all important features of depression. Indeed, previous studies of patients with major depression have reported high SANS scores (7–9). From our clinical work we gained the impression that a large number of schizophrenic patients are somewhat aware of their negative symptoms, but we also gained the impression that they are less aware of these impairments than patients with a depressive disorder and that they are less concerned about them. The objectives of this study, therefore, were to test three hypotheses: 1) schizophrenic patients would report more impairments on a self-rating scale for negative symptoms than normal subjects and attribute higher levels of distress to these impairments; 2) schizophrenic patients would report fewer impairments than patients with a depressive disorder and attribute lower levels of distress to these impairments; and 3) schizophrenic patients would attribute their impairments less often to mental illness than would patients with a depressive disorder.

METHOD

The 33 normal subjects (17 men and 16 women) were recruited from two classes in a school for psychiatric nursing. Their mean age was 25.6 years (SD=5.6, range=18–35). Before admission to the school they had had an interview and a medical examination, neither of which had revealed evidence of a major psychiatric disorder. The students were informed that the Subjective Experience of Negative Symptoms scale is used for patients with psychiatric disorders and that it would be useful to know how other people respond. All students agreed to participate.

The 86 schizophrenic patients (60 men and 26 women) were recruited from the medium- and long-stay wards of the Rosenburg Psychiatric Hospital in The Hague and the Joris Psychiatric Hospital in Delft, The Netherlands. The DSM-III-R diagnosis of schizophrenia had been made by the responsible psychiatrist and was checked by the first author. If there was any doubt about the diagnosis, the patient was not accepted for the study. Patients who had a physical handicap that explained their impaired functioning, patients with few negative symptoms (fewer than two global ratings of at least 2 on the SANS subscales for affective flattening, alogia, avolition-apathy, and asociality-anhedonia), and patients over 65 years of age were excluded. Other reasons for exclusion were the presence of mental subnormality (defined as failure to complete primary education or having repeated more than one grade at primary school), an organic mental disorder (DSM-III-R), recent or current substance abuse (DSM-III-R), a current manic or major depressive episode (DSM-III-R), a first language other than Dutch, and incomprehensible speech. All eligible patients were approached for the study. Four patients were unable to complete the Subjective Experience of Negative Symptoms scale on account of serious attentional deficits.

Thirty-one schizophrenic patients refused to take part. They did not differ significantly from the patients who participated with regard to age, sex, level of education, length of illness, or length of current admission (two-tailed chi-square tests or t tests). A description of the final study group is given in table 1. Forty-nine patients (57%) had achieved at least a 10th-grade education (compared to 10, or 50%, in the group with a depressive disorder). Five patients were taking clozapine. The mean dose of classic neuroleptics for the remaining patients, converted into equivalents of haloperidol, was 21.9 mg/day (SD=27.3).

The 20 patients with a depressive disorder (five men and 15 women) were recruited from Bloemendaal Psychiatric Centre, The Hague. The DSM-III-R diagnosis was made by the second author and confirmed by another psychiatrist. In order to match this group of patients to the schizophrenic group with regard to severity of negative symptoms, we selected patients with a relatively severe form of disorder. To this end, we approached all of the patients in two wards who met the DSM-III-R criteria for a major depressive episode and who, in the week before the study, had scored at least 18 on the 17-item version of the Hamilton Depression Rating Scale (10). There were no refusals. With the exception of one patient who was diagnosed with bipolar disorder, depressive episode, all patients had a unipolar disorder. The depression was moderately severe in seven patients, severe in nine, and “psychotic, with mood-congruent features” (DSM-III-R) in four. The criteria for exclusion were the same as those applied to the patients with schizophrenia (except, of course, for the presence of a major depressive episode). Eleven patients were taking tricyclic antidepressants; three were taking tranylcypromine. Five patients were taking low doses of antipsychotic medication (equivalent to 1–4 mg/day of haloperidol). None of the patients was taking clozapine.

After complete description of the study, written informed consent was obtained from all patients who agreed to participate.

The Subjective Experience of Negative Symptoms Scale

Self-ratings on this scale are elicited in a semistructured interview. The interviewer gives a standardized explanation of each item in everyday language and asks a first question, for instance, “How much energy do you have?” Next, the interviewer hands the patient a card that lists five alternative answers: 1) very little, 2) little, 3) average, 4) a lot, and 5) very much. The patient must choose one answer. He is instructed to compare himself to people of his age who have not been admitted to a psychiatric hospital and is reminded of this instruction at four points during the interview. Having asked the first question for all 21 items on the scale, the interviewer asks two more questions about the items that elicited a rating of 1 or 2 (i.e., the patient indicated the presence of the symptom). The purpose of the second (open-ended) question is to collect information regarding the patient's attributions. Finally, the interviewer asks the patient whether he is bothered or distressed by the symptom (question 3a). If the answer is affirmative, the patient is asked how much he is bothered or distressed (question 3b) and is given a card listing five alternative answers: 1) very little, 2) little, 3) quite a lot, 4) much, and 5) very much. The three questions constitute the three parts of the Subjective Experience of Negative Symptoms scale (awareness, attribution, and distress). The rating procedure for the scale has two important advantages over one in which the interviewer decides to what extent the patient is aware of a symptom. First, there is no risk of interpretation bias. Second, the ratings are independent of the amount of the patient's spontaneous speech. The items “blocking” and “poverty of content of speech” and the items measuring attention were not included in the Subjective Experience of Negative Symptoms scale and were not rated on the SANS because they do not seem to pertain to the negative syndrome (11).

Procedure

The patients were interviewed twice. In one session they completed the Subjective Experience of Negative Symptoms scale with the help of a research assistant. In the other session they met the psychiatrist, who completed the SANS (6) and the Montgomery-Åsberg Depression Rating Scale (12). The order of the sessions was random, and the interval was kept as short as possible (maximum of 1 week). The ratings of patients with schizophrenia and those with a depressive disorder were made by the first and second authors, respectively. Before the start of the study, in order to ensure a degree of conformity of assessment, the authors compared their ratings of five patients with a depressive disorder. The level of agreement was largely sufficient for the purposes of this study (the intraclass correlation coefficient was 0.85 for the SANS summary score and 0.98 for the total Montgom~ery-Åsberg Depression Rating Scale score). To help the psychiatrists make their ratings, nurses provided detailed written information on the patients' daily activities. To control for diurnal variation in mood, the interviews with the depressed patients were conducted in the afternoon.

The students were able to complete the Subjective Experience of Negative Symptoms scale without the help of a research assistant and rated themselves during a classroom period. To protect each student's privacy, the tables in the classroom were arranged in such a way that nobody could see his or her neighbor's self-ratings. The students did not give their names, only their age and sex. This procedure guaranteed anonymity. The students were instructed to compare themselves to people of their age. They were asked the first and third questions of the scale, relating to awareness and distress, respectively. They were not asked the second question (about attributions) and were not assessed on “objective” scales.

The time frame for all measurements was 1 week.

Analysis

Global ratings for affective flattening, alogia, avolition-apathy, and asociality-anhedonia were added together to provide a SANS summary score. Differences between the two groups of patients in age, length of illness, length of current admission, SANS summary scores, and total Montgomery-Åsberg Depression Rating Scale scores were examined by using two-tailed t tests for independent samples. Self-ratings in response to the first question on the Subjective Experience of Negative Symptoms scale were added to provide a total score for that scale. A total score for disruption and distress was obtained by adding all scores for question 3b.

First hypothesis. The students were younger than the schizophrenic patients, and more of them were female. Consequently, differences in Subjective Experience of Negative Symptoms total scores and distress scores were examined by using analysis of covariance (ANCOVA), with age and sex as covariates.

Second hypothesis. Differences in Subjective Experience of Negative Symptoms total scores and distress scores between the two groups of patients were also examined with ANCOVA. To control for the important clinical differences between patients with schizophrenia and those with a depressive disorder, age, sex, length of illness, length of current admission, dose of neuroleptic medication (expressed in equivalents of haloperidol), use of clozapine (yes/no), and SANS summary score were entered as covariates. As the distributions for length of current admission and dose of neuroleptic medication were skewed to the right, the logarithms (base 10) of these variables were used. The assumptions for adequate use of ANCOVA, especially with regard to entering the covariates into the model, were checked and found to be justified. Regression slopes between outcome variables and covariates did not differ significantly between the two diagnostic groups.

To examine whether differences in Subjective Experience of Negative Symptoms total scores reflect differences of opinion between the patient and the psychiatrist, an additional analysis was carried out. Self-assessments were classified as true positive, true negative, false positive, or false negative. True positive and true negative self-reports indicated agreement between the patient and the psychiatrist on the presence and absence of negative symptoms, respectively. In the case of false positive self-reports, the patient reported the symptom, whereas the psychiatrist gave a SANS rating of 0 (absent) or 1 (dubious). False negative self-reports indicated that the patient did not report the symptom, whereas the psychiatrist gave a rating of 2 (mild, but definite) or higher. (Designation of self-reports as false or true does not necessarily mean, of course, that the psychiatrists' ratings were always perfectly valid.)

Third hypothesis. The first author studied attributions (replies to the second question on the Subjective Experience of Negative Symptoms scale) for symptoms that had received a SANS rating of at least 2 (mild, but definite) and investigated how often patients viewed these symptoms as a manifestation of mental illness. A previous study using the Subjective Experience of Negative Symptoms scale showed that this could be done reliably (5). Attributions were regarded as attributions to mental illness when the patient ascribed the symptom to a psychiatric disorder (e.g., schizophrenia or depression) or to some form of psychological dysfunction (e.g., psychosis, confusion, inner tension, low mood). The rate of this kind of attribution was expressed as a percentage of all attributions in each group of patients. The difference in proportions was examined by means of a chi-square test (with Yates's correction). The statistical tests relating to the three hypotheses were one-tailed. All other tests were two-tailed.

RESULTS

It is important to bear in mind that low total scores on the Subjective Experience of Negative Symptoms scale indicate that subjects report many impairments, whereas high distress scores indicate that they report high levels of distress.

First hypothesis. As expected, total scores on the Subjective Experience of Negative Symptoms scale were lower for the schizophrenic patients than for the normal students, and the opposite was true for distress scores. ANCOVA, controlling for sex and age, showed a highly significant effect of diagnosis on both scores (table 2).

Second hypothesis. The two groups of patients did not differ significantly in SANS summary scores (table 1). As expected, total scores on the Subjective Experience of Negative Symptoms scale for the patients with a depressive disorder were lower than those for the schizophrenic patients, and their distress scores were much higher. ANCOVA revealed that these differences remained significant after we controlled for age, sex, length of illness, length of current admission, dose of neuroleptic medication, use of clozapine, and SANS summary score (table 2). Since a large number of covariates increases the risk of multicollinearity, we repeated the ANCOVAs after one-by-one elimination of covariates, until the p values of all covariates in the model were lower than 0.15. With this procedure the F ratios remained highly significant.

As the higher rate of reported impairments in the group of patients with a depressive disorder might reflect a tendency toward overreporting rather than a better awareness, the results presented in table 3 are of interest. The results suggest that the lower total scores on the Subjective Experience of Negative Symptoms scale of the patients with a depressive disorder are probably due more to a higher rate of true positive replies than to a higher rate of false positive ones.

The differences in the rates of self-reported impairments become even more marked when the numbers of reported symptoms (i.e., ratings of 1 or 2 in response to the first question on the Subjective Experience of Negative Symptoms scale) are considered. The students reported an average of 2.7 negative symptoms (SD=3.2) on the 21-item scale. This figure was 7.4 (SD=4.5) for the schizophrenic patients and 13.2 (SD=5.2) for the patients with a depressive disorder. ANCOVA, controlling for sex and age, showed that these differences were highly significant (F=26.5, df=2,136, p<0.001).

Third hypothesis. The rate of attributions to mental illness was 2.8% (14 of 504 replies) among the schizophrenic patients and 32.8% (76 of 232 replies) among the patients with a depressive disorder. The difference was statistically significant (χ²=114.3, df=1, p<0.001, with Yates's correction).

DISCUSSION

The hypotheses were supported. The schizophrenic patients reported more impairments and more distress than the normal subjects. However, they reported fewer impairments and less distress than the patients with a depressive disorder who had a similar score on the SANS.

These differences remained statistically significant after we controlled for a large number of clinical variables. The schizophrenic patients also attributed their impairments less often to mental illness than did the patients with a depressive disorder. The Subjective Experience of Negative Symptoms scale was thus validated by the contrasted groups method (13).

The large age difference between the normal subjects and the schizophrenic patients is unlikely to have confounded the findings, because the effects of diagnosis remained highly significant after we controlled for age. Furthermore, field studies of subjects aged 18–65 do not reveal a strong age effect on self-ratings for psychiatric problems. Scores on the General Health Questionnaire, for instance, are only weakly related to age (14). In this study total scores and distress scores on the Subjective Experience of Negative Symptoms scale did not correlate significantly with age in any of the three groups studied (Pearson's correlations, two-tailed p values >0.37). The procedures for data collection among students and patients were somewhat different. The students gave their ratings anonymously, whereas the patients had a face-to-face interview. One might suggest, therefore, that a tendency to give socially desirable replies is somewhat stronger in the latter situation. However, if this tendency was of any influence at all, it would have reduced the difference between the students and the schizophrenic patients, not increased it.

Since the patients with schizophrenia did not assess themselves as the normal subjects did, they were probably at least somewhat aware of their negative symptoms. On the other hand, since their self-assessments were less realistic than those of the patients with a depressive disorder, the results confirm and enlarge upon previous findings regarding schizophrenic patients' impaired insight into negative symptoms (3, 4) and their relative lack of concern about these symptoms (9). These findings may have implications for diagnosis. Clinical experience indicates that differentiation between depressive syndromes and negative syndromes is often difficult. The results presented here suggest that an exploration of three aspects of the experience of symptoms (i.e., awareness, attribution, and distress) may be helpful.

A limitation of the study is that the patients were more severely impaired than those in the community, and most patients had not participated in psychoeducational programs. Patients with a milder type of disorder or patients who have followed these programs may have more insight into negative symptoms. Furthermore, several schizophrenic patients refused to participate. It follows that the results should be interpreted with caution and cannot be generalized to all schizophrenic patients.

TABLE 1

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TABLE 2

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TABLE 3

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