SEARCH

SEARCH BY CITATION

Keywords:

  • cognitive dysfunction;
  • depressive and negative symptoms;
  • objective quality of life;
  • schizophrenia;
  • subjective quality of life

Abstract

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENT
  7. REFERENCES

Aim:  In recent years, greater attention has been given to quality of life (QOL) in schizophrenia and several studies reported that negative and depressive symptoms and cognitive dysfunction are related to patient QOL. But because a variety of QOL measures have been used in the previous studies, there seems to be no unanimous predictors for subjective and objective QOL. The purpose of the present study was to elucidate the relationship between clinical variables and subjective and objective QOL in outpatients with schizophrenia, using schizophrenia disease-specific QOL measures. Particular attention was paid to cognitive function as a predictor of QOL.

Methods:  Schizophrenia symptoms of the Positive and Negative Syndrome Scale (PANSS) were divided into five factors: positive factor, negative factor, cognitive factor, emotional discomfort, and hostility. The study sample consisted of 84 schizophrenia outpatients. Subjective and objective QOL were assessed with Schizophrenia Quality of Life Scale (SQLS) and the Quality of Life Scale (QLS), respectively.

Results:  Subjective QOL correlated significantly with emotional discomfort, positive factor, negative factor, extrapyramidal symptoms and cognitive factor, while objective QOL correlated with negative factor, cognitive factor, emotional discomfort, extrapyramidal symptoms, and dose of antipsychotics. Total score and three of four subscales in the QLS correlated significantly with cognitive factor, while cognitive factor had a significant correlation with only one of three scales of SQLS. Stepwise regression showed that subjective QOL was significantly predicted by emotional discomfort and extrapyramidal symptoms, while negative factor was the most important predictor of objective QOL.

Conclusion:  Cognitive dysfunction had a greater influence on objective QOL than subjective QOL. Treating depressive and negative symptoms and extrapyramidal symptoms might contribute to enhanced subjective and objective QOL.

OVER THE PAST two decades, the concept of quality of life (QOL) has become an important attribute in patient care and clinical research.1,2 Although there seems to be no unanimous definition of QOL, QOL is generally thought to include life satisfaction, social functioning, daily living activities, and physical health, and it has been recognized as an important indicator of how well patients with schizophrenia can function.2–4 QOL has been measured from two different viewpoints. One is subjective QOL, rated by patients themselves, and the other is objective QOL, rated by observers. Objective measures of QOL include indicators of health and living conditions, sociodemographic items and role functioning, whereas subjective indicators of QOL measure life satisfaction in general and within different life domains. Because patients with schizophrenia were thought to be unable to assess their QOL themselves because of their cognitive deficit function, objective QOL have been frequently used in many studies and the evaluation of treatments for schizophrenia was mainly based on objective assessment of the psychotic symptoms. But now there is general agreement that symptomatically stabilized patients are able to evaluate their QOL themselves.5

The clinical factors related to levels of QOL have been variously reported. Several studies including our own have suggested that depressive mood may be the most important determinant for subjective QOL.6–11 Other studies reported that positive symptoms12 or akathisia symptoms as well as the total severity of psychopathology1 predicted subjective QOL.

In some studies, the severity of negative symptoms7,10,11,13 or the presence of tardive dyskinesia14 was reported to be associated with a poor objective QOL. Levels of insight into the illness showed no significant relationship with QOL levels.15 In addition to clinical symptoms, sociodemographic factors also influence objective QOL of patients with schizophrenia.16

In recent years, greater attention has been given to the cognitive dimension in schizophrenia. One of the reasons is that atypical antipsychotics improve cognitive function while conventional antipsychotics produce minimal cognitive improvement.17,18 Several studies strongly indicate that cognitive function has a greater impact on QOL in patients with schizophrenia than do positive symptoms.19–21 Executive functioning and verbal learning appear to be especially valid predictors of work status.19,22–24 Other studies reported that unemployed patients with schizophrenia were impaired on measures of memory and problem solving, even when IQ was within an average range.25,26

The purpose of the present study was to further elucidate clinical determinants of both subjective and objective QOL. In the present study, subjective and objective QOL were assessed on the Schizophrenia Quality of Life Scale (SQLS)27,28 and the Quality of Life Scale (QLS),29,30 respectively. Schizophrenia symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS).31 Evidence from recent factor analysis studies conducted with PANSS has suggested that a five-dimensional structure appears to be a better representation of the psychopathological data. Analysis for the present study is based on five orthogonal dimensions according to Bell et al.:32 positive factor, negative factor, cognitive factor, emotional discomfort, and hostility. Contribution of these five symptom factors as well as duration of illness, number of hospitalizations, dose of antipsychotics and extrapyramidal symptoms to the levels of QOL was investigated. Few studies have investigated the relationship between subjective and objective QOL and the five PANSS factors. Particular interest was paid to the PANSS cognitive factor as a predictor of subjective or objective QOL.

METHODS

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENT
  7. REFERENCES

Subjects

Clinical data were collected at Department of Psychiatry, Tokushima University Hospital from 18 May to 5 August 2005. After obtaining written consent from all subjects, we investigated a sample of 105 outpatients whose diagnosis was confirmed by at least two psychiatrists according to the DSM-IV.33

Subjects were excluded if they presented with any organic central nervous system disorder, epilepsy, mental retardation, severe somatic disorder, drug dependence, or alcohol dependence. Of 105 patients, 84 completed the questionnaire.

The present subjects were all clinically stable and received outpatient treatment regularly. Seventy-two had never been hospitalized during the previous 1 year including 28 who had never had inpatient treatment, while 12 had inpatient treatment during the previous 1 year. The antipsychotic regimen of 75 subjects had been unchanged for at least 6 months before the recruitment, and only nine subjects had a little change in regimen during the previous 6 months, but the nine were judged as clinically stabilized by the treating psychiatrists.

Procedure

To assess subjective QOL, we used the SQLS.27,28 Objective QOL was evaluated using the QLS.29,30 Psychotic symptoms were evaluated using the PANSS.31 Drug-induced extrapyramidal symptoms were assessed using the Drug-Induced Extrapyramidal Symptoms Scale (DIEPSS).34

The SQLS is a self-reported, 30-item questionnaire for measuring QOL specific to patients with schizophrenia with good reliability and validity.27,28 It is composed of three scales: psychosocial, motivation/energy and symptoms/side-effects. Lower scores indicate higher levels of subjective QOL.

The QLS assesses objective QOL by means of a semistructured interview. The reliability and validity of the scale has been verified.29,30 The ratings are based upon patient self-report and observer judgment about patient functioning and life circumstances. This instrument has four subscales: interpersonal relations, instrumental role, intrapsychic foundation, and common objects and activities. Higher scores indicate higher levels of objective QOL. Some of the authors, who are all experienced psychiatrists, conducted the interviews according to the Evaluation Manual for the QLS.30

The PANSS was originally designed as a rating scale that represents positive, negative and general psychopathology.31 The score ranges are 30–210 for the global score; 7–49 for the positive score; 7–49 for the negative score; and 16–112 for the general psychopathology score. A breakdown into five factors was used according to Bell et al.:32 positive factor (score range 6–42; items: delusions, hallucinations, grandiosity, suspiciousness, somatic concern, unusual thought content); negative factor (score range 8–56; items: blunted affect, emotional withdrawal, poor rapport, passive social withdrawal, lack of spontaneity, motor retardation, disturbance of volition, preoccupation); cognitive factor (score range 7–49; items: difficulty in abstract thinking, stereotyped thinking, conceptual disorganization, lack of judgment and insight, poor attention, tension, mannerisms and posturing); emotional discomfort factor (score range 4–28; items: depression, anxiety, guilt feeling, active social avoidance); and hostility factor (score range 4–28; items: excitement, hostility, poor impulse control, uncooperativeness).

The DIEPSS is composed of eight individual parameters (gait, bradykinesia, sialorrhea, muscle rigidity, tremor, akathisia, dystonia, and dyskinesia) and one global assessment constructed to assess extrapyramidal adverse effects, using a 5-point scale that ranges from 0 to 4 (0, none; 4, severe). The reliability and validity of the scale have been verified.34

All the scales except the SQLS were applied by the authors, who were experienced psychiatrists. Interrater consistencies of all the scales in our group have been shown to be satisfactory.35

Statistical analysis

Pearson's correlation coefficients were calculated to study the relationship between subjective and objective QOL and clinical variables (duration of illness, number of hospitalizations, dose of antipsychotics, PANSS positive symptoms score, PANSS negative symptoms score, PANSS cognitive score, PANSS emotional discomfort score, PANSS hostility score and the DIEPSS score). Because data were normal continuous variables except for the PANSS positive symptoms score, duration of illness and dose of antipsychotics, and because the sample size was large, we used parametric test. Then, using clinical variables that showed significant correlation, stepwise regression was done to determine which clinical variables were the best predictors for each dependent variable. The SQLS score and the QLS total score and subscales were chosen as dependent variables. Statistical analysis was done using SPSS version 11.5J (SPSS, Chicago, IL, USA).

RESULTS

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENT
  7. REFERENCES

Demographic characteristics and means and standard deviations of the clinical indices are presented in Table 1. All subjects were Japanese, and 42 were male and 42 were female. We used the chlorpromazine conversion chart36 to determine the dosage of antipsychotic medication.

Table 1.  Subject characteristics (mean ± SD)
  • Chlorpromazine equivalent.

  • DIEPSS, Drug-Induced Extrapyramidal Symptoms Scale; PANSS, Positive and Negative Syndrome Scale; QLS, Quality of Life Scale; SQLS, Schizophrenia Quality of Life Scale.

n (M/F)84 (42/42)
Age (years)40.7 ± 12.6
Duration of illness (years)14.6 ± 10.4
No. hospitalizations1.4 ± 1.6
Dose of antipsychotics (mg/day)534 ± 542
Type of schizophrenia (n)Paranoid65
Residual13
Disorganized1
Catatonic4
Undifferentiated1
Marital state (n)Married19
Never married63
Divorced2
PANSSTotal61.7 ± 11.7
Positive factor12.1 ± 4.9
Negative factor21.1 ± 6.9
Cognitive factor14.4 ± 5.5
Emotional discomfort5.6 ± 2.1
Hostility8.3 ± 2.5
DIEPSS (Overall) 1.3 ± 2.3
SQLSPsychosocial24.3 ± 10.7
Motivation/energy14.3 ± 4.6
Symptoms/side-effects7.9 ± 4.7
QLSTotal65.4 ± 22.9
Interpersonal Relations21.2 ± 10.6
Instrumental Role13.2 ± 5.0
Intrapsychic Foundations23.6 ± 8.0
Common Objects and Activities7.3 ± 2.0

The correlations between the SQLS scores and clinical variables are shown in Table 2. Only positive factor and emotional discomfort were correlated significantly with the score of psychosocial scale. The score of the motivation and energy scale correlated significantly with positive factor, negative factor and emotional discomfort. Positive factor, cognitive factor, and extrapyramidal symptoms were correlated significantly with the score of the symptoms and side-effects scale.

Table 2.  SQLS scores and clinical variables
 SQLS
PsychosocialMotivation/energySymptoms/side-effects
  • *

    P < 0.05;

  • **

    P < 0.01;

  • ***

    P < 0.001, Pearson correlations.

  • DIEPSS, Drug-Induced Extrapyramidal Symptoms Scale; PANSS, Positive and Negative Syndrome Scale; SQLS, Schizophrenia Quality of Life Scale.

PANSS
 Positive factor0.274*0.227*0.260*
 Negative factor0.1840.293**0.056
 Cognitive factor0.190.1760.266*
 Emotional discomfort0.449***0.408***0.195
 Hostility0.1520.1410.120
DIEPSS0.2040.1790.279*
Duration of illness0.170−0.1110.140
Number of hospitalization0.149−0.0160.151
Dose of antipsychotics0.2100.0110.047

The correlations between the scores of the QLS total and subscales and clinical variables are shown in Table 3. Negative factor was correlated with total and all subscales. Total score and three subscales of four correlated with cognitive factor.

Table 3.  QLS total and subscale scores and clinical variables
 QLS
TotalInterpersonal relationsInstrumental roleIntrapsychic foundationCommon objects and activities
  • *

    P < 0.05;

  • **

    P < 0.01;

  • ***

    P < 0.001, Pearson correlations.

  • DIEPSS, Drug-Induced Extrapyramidal Symptoms Scale; PANSS, Positive and Negative Syndrome Scale; QLS, Quality of Life Scale.

PANSS
 Positive factor−0.098−0.059−0.143−0.110−0.002
 Negative factor−0.535***−0.487***−0.340**−0.584***−0.337**
 Cognitive factor−0.303**−0.228*−0.267*−0.350**−0.177
 Emotional discomfort−0.272*−0.263*−0.208−0.269*−0.121
 Hostility−0.022−0.039−0.022−0.0250.108
DIEPSS−0.252*−0.241*−0.206−0.207−0.248*
Duration of illness−0.043−0.0530.137−0.128−0.038
Number of hospitalization0.003−0.0460.0130.0230.149
Dose of antipsychotics−0.272*−0.258*−0.253*−0.222*−0.210

Table 4 shows the results of stepwise regression on the SQLS and the QLS.

Table 4.  Stepwise regression for SQLS and QLS
 Dependent variableIndependent variableAdjusted R2β
  • *

    P < 0.05;

  • **

    P < 0.01;

  • ***

    P < 0.001.

  • DIEPSS, Drug-Induced Extrapyramidal Symptoms Scale; QLS, Quality of Life Scale; SQLS, Schizophrenia Quality of Life Scale.

SQLSPsychosocialEmotional discomfort0.191***0.449***
Motivation/energyEmotional discomfort0.156***0.408***
Symptoms/side-effectsDIEPSS0.067**0.279**
QLSTotalNegative factor0.334***−0.504***
Dose of antipsychotics−0.190*
Interpersonal RelationsNegative factor0.228***−0.487***
Instrumental RoleNegative factor0.105**−0.340**
Intrapsychic FoundationsNegative factor0.333***−0.584***
Common Objects and ActivitiesNegative factor0.180***−0.337**

The psychosocial scale score and the motivation/energy scale score were significantly predicted only by emotional discomfort. The symptoms/side-effects scale score was significantly predicted only by extrapyramidal symptoms.

The QLS total score was predicted independently by negative factor and dose of antipsychotics. Four subscales were predicted independently by negative factor.

DISCUSSION

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENT
  7. REFERENCES

In recent years, greater attention has been given to QOL in schizophrenia and several symptoms have been reported to be related to patient QOL. But in the < previous studies, because a variety of QOL measures have been used, there seems to be no unanimous predictors for subjective and objective QOL. The purpose of the present study was to elucidate the relationship between clinical variables and subjective and objective QOL, using PANSS five-factor analysis and schizophrenia disease-specific QOL measures. Several recent studies strongly indicate that cognitive function has a greater impact on QOL in patients with schizophrenia than do positive symptoms.19–21 Therefore we paid particular attention to the PANSS cognitive factor and explored the relationship between cognitive dysfunction and patient QOL.

The clinical factors related to levels of QOL have been variously reported. For the clinical factors associated with subjective QOL, Dickerson et al. found that patients' subjective QOL measured by the Quality of Life interview was related to the depression factor in PANSS.6 Huppert et al. reported that more severe depression as rated on the brief Psychiatric Rating Scale (BPRS) was associated with lower subjective QOL measured by the Quality of Life interview.8 Fitzgerald et al. reported that subjectively reported life satisfaction was more influenced by depressive symptom on the Montgomery–Asberg Depression Rating Scale (MADRS) than positive symptom or negative symptom.7 Other similar studies including our own also support the association of depressive symptom with subjective QOL.9–11 In the present study, emotional discomfort and positive factor were correlated with psychosocial scale scores of SQLS, and stepwise regression showed that emotional discomfort predicted the psychosocial score. Emotional discomfort, negative factor and positive factor were correlated with motivation/energy scores of SQLS, and stepwise regression showed that emotional discomfort predicted the motivation/energy scale score. The present results are consistent with those reported by Tomotake et al. and Aki et al., who assessed subjective QOL and depressive symptoms with SQLS and the Calgary Depression Scale for Schizophrenia, respectively.10,11

In the current study, drug-induced extrapyramidal symptoms, cognitive factor, and positive factor were correlated with symptoms/side-effects scale scores of SQLS, and stepwise regression showed that drug-induced extrapyramidal symptoms predicted the symptoms/side-effects scale score. The present result suggests that the extrapyramidal symptom is a factor negatively influencing subjective QOL. The influence of extrapyramidal adverse effects has already been documented. Ritsner et al., using the MADRS, the Talbieh Brief Distress Inventory (TBDI), the Abnormal Involuntary Movement Scale (AIMS) and the Quality of Life Enjoyment and Satisfaction Questionnaire in schizophrenia patients, reported that the depression score on the TBDI and the score at the AIMS were predictors of poor QOL.37 Awad et al. reported that, using PANSS, Hillside Akathisia scale and the Drug Attitude Inventory, subjective QOL is greatly influenced by psychopathology, akathisia and patients' subjective tolerance of medications, and concluded that effort should be directed towards effective control of psychotic symptoms and minimizing the side-effects of antipsychotic drugs in order to improve the QOL of schizophrenia patients.1 These two studies, however, used subjective QOL measures, which, unlike SQLS, did not have a subscale focused on symptoms/side-effects. The current study suggests that patients with drug-induced extrapyramidal symptoms have subjective discomfort with respect to their symptoms and side-effects.

The present study suggests that negative symptoms predict objective QOL (QLS total and all the subscales). The present results are consistent with those reported by Tomotake et al. and Aki et al., who assessed objective QOL and negative symptoms using QLS and BPRS, respectively.10,11 Considering that QLS was originally designed to assess deficit symptoms and the dysfunctions related to them,29 the correlation between negative symptoms and QLS scores seems to be reasonable.

The influence of negative symptoms on objective QOL has already been documented. Fitzgerald et al., using QLS, PANSS and MADRAS, indicated a significant positive relationship between all of the four QLS subscales and PANSS negative scores, but none of the QLS subscales was related significantly to PANSS positive scores and MADRAS scores.7 Norman et al., using QLS, Scale for the Assessment of Positive Symptoms and Scale for the Assessment of Negative Symptoms (SANS), reported that negative symptom, level of functioning and positive symptom related to the scores on QLS and that QLS was most strongly related to negative symptom.12 Browne et al. also investigated the relationship between objective QOL assessed with QLS and clinical variables, and reported that total QLS score correlated significantly with negative symptom rated with SANS.14

Greater attention has been given to the cognitive dimension in schizophrenia in recent years. Several studies strongly indicate that cognitive function has a greater impact on QOL in patients with schizophrenia than do positive symptoms.19–21 Bell et al. found that higher scores on PANSS cognitive component were significantly correlated with poorer performance on neuropsychological tests.32,38 Hofer et al. reported that, using the cognition subscale of the PANSS, poorer cognition scores reduced the competitive employment and that PANSS cognition subscale as well as negative symptom and positive symptom were found to contribute significantly to the Global Assessment of Functioning score.39 Consistent with these previous studies, the QLS total score and all the subscale scores of QLS except common objects and activities subscale correlated significantly with PANSS cognitive score in the present study. Although stepwise regression showed that negative factor alone significantly predicted objective QOL, cognitive function also had an apparent influence on it. But Hofer et al. found that clinical assessment of cognitive deficits on PANSS is not a viable alternative to neuropsychological testing to obtain information about cognitive functioning in schizophrenia.40 Their finding limits the interpretation of the present results. To elucidate influence of the cognitive dysfunction on QOL, further studies using neuropsychological tests such as Brief Assessment of Cognition in Schizophrenia41 are necessary.

In contrast, in the present study, cognitive dysfunction did not predict subjective QOL, although the symptoms/side-effects scale score of SQLS was significantly correlated with cognitive dysfunction. Consistent with the present result, Reine et al. reported that only one of eight subscales in the short version of the Lehman quality of life scale correlated with PANSS cognitive factor, while five subscales correlated with PANSS depression factor.9 Karow et al. reported that on longitudinal study, only one subscale of five in the short form of the subjective Well-being under Neuroleptics Scale (SWN) correlated with PANSS cognitive factor in the acute and mid-term phase, while PANSS depression factor correlated with total scores of SWN in the acute, mid-term, and long-term phase.42 These reports, including our own, suggest that cognitive dysfunction has little association with subjective QOL. It seems that cognitive dysfunction has apparent influence on objective but not subjective QOL.

Considering the results of previous studies as well as the present study, active treatment for depressive and negative symptoms and extrapyramidal symptoms is recommended to improve patient QOL. From this point, atypical antipsychotics are perceived to be more effective and have fewer adverse effects than typical antipsychotics.17,18 The influence of atypical antipsychotics on QOL has already been documented. Using QLS, SQLS, BPRS and DIEPSS, Taniguchi et al. reported that the replacement of previous drugs including both typical and atypical antipsychotics with quetiapine improved patients' subjective and objective QOL, clinical symptoms and extrapyramidal symptoms, although they did not comment on the improvement of depressive symptoms.43 In contrast, a randomized controlled trial provided evidence that typical antipsychotics showed an improvement in QLS score and PANSS total and positive, negative and general symptoms, and concluded that there is no disadvantage across 1 year in terms of QOL and symptoms in using typical antipsychotics rather than atypical antipsychotics.44 Further well-controlled studies are necessary to elucidate the influence of antipsychotics on QOL.

In summary, we have examined the relationship between clinical factors and QOL in schizophrenia outpatients in the chronic phase with schizophrenia disease-specific subjective and objective QOL measures. Consistent with past report, the results indicate that depressive symptoms and extrapyramidal symptoms predict subjective QOL and that negative symptoms predict objective QOL. The present results also showed that cognitive dysfunction had an apparent influence on objective but not subjective QOL. Active treatment for depressive and negative symptoms and extrapyramidal symptoms is recommended to improve patient QOL.

ACKNOWLEDGMENT

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENT
  7. REFERENCES

The authors wish to thank Mrs K. Kikuchi for her help with data collection.

REFERENCES

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENT
  7. REFERENCES
  • 1
    Awad AG, Voruganti LN, Heslegrave RJ. A conceptual model of quality of life in schizophrenia: Description and preliminary clinical validation. Qual. Life Res. 1997; 6: 2126.
  • 2
    Lehman AF. A quality of life interview for the chronically mentally ill. Eval. Program Plann. 1998; 11: 5162.
  • 3
    Meltzer HY. Dimensions of outcome with clozapine. Br. J. Psychiatry Suppl. 1992; 17 (Suppl.17): 4653.
  • 4
    Meltzer HY. Outcome in schizophrenia: Beyond symptom reduction. J. Clin. Psychiatry 1999; 60: 37.
  • 5
    Voruganti L, Heslegrave R, Awad AG et al. Quality of life measurement in schizophrenia: Reconciling the quest for subjectivity with the question of reliability. Psychol. Med. 1998; 28: 165172.
  • 6
    Dickerson FB, Ringel NB, Parente F. Subjective quality of life in out-patients with schizophrenia: Clinical and utilization correlates. Acta Psychiatr. Scand. 1998; 98: 124127.
  • 7
    Fitzgerald PB, Williams CL, Corteling N et al. Subject and observer-rated quality of life in schizophrenia. Acta Psychiatr. Scand. 2001; 103: 387392.
  • 8
    Huppert JD, Weiss KA, Lim R et al. Quality of life in schizophrenia: Contributions of anxiety and depression. Schizophr. Res. 2001; 51: 171180.
  • 9
    Reine G, Lancon C, Di Tucci S et al. Depression and subjective quality of life in chronic phase schizophrenic patients. Acta Psychiatr. Scand. 2003; 108: 297303.
  • 10
    Tomotake M, Kaneda Y, Iga J et al. Subjective and objective measures of quality of life have different predictors for people with schizophrenia. Psychol. Rep. 2006; 99: 477487.
  • 11
    Aki H, Tomotake M, Kaneda Y et al. Subjective and objective quality of life, levels of life skills, and their clinical determinants in outpatients with schizophrenia. Psychiatry Res. 2008; 158: 1925.
  • 12
    Norman RMG, Malla AK, Mclean T et al. The relationship of symptoms and level of functioning in schizophrenia to general wellbeing and the Quality of Life Scale. Acta Psychiatr. Scand. 2000; 102: 303309.
  • 13
    Strejilevich SA, Palatnik A, Avila R et al. Lack of extrapyramidal side effects predicts quality of life in outpatients treated with clozapine or with typical antipsychotics. Psychiatry Res. 2005; 133: 277280.
  • 14
    Browne S, Roe M, Lane A et al. Quality of life in schizophrenia: Relationship to sociodemographic factors, symptomatology and tardive dyskinesia. Acta Psychiatr. Scand. 1996; 94: 118124.
  • 15
    Browne S, Garavan J, Gervin M et al. Quality of life in schizophrenia: Insight and subjective response to neuroleptics. J. Nerv. Ment. Dis. 1998; 186: 7478.
  • 16
    Caron J, Mercier C, Diaz P et al. Socio-demographic and clinical predictors of quality of life in patients with schizophrenia or schizo-affective disorder. Psychiatry Res. 2005; 137: 203213.
  • 17
    Voruganti L, Cortese L, Oyewumi L et al. Comparative evaluation of conventional and novel antipsychotic drugs with reference to their subjective tolerability, side-effect profile and impact on quality of life. Schizophr. Res. 2000; 16: 135145.
  • 18
    Davis JM, Chen N, Glick ID et al. A meta-analysis of the efficacy of second-generation antipsychotics. Arch. Gen. Psychiatry 2003; 60: 553564.
  • 19
    Green MF. What are the functional consequences of neurocognitive deficits in schizophrenia? Am. J. Psychiatry 1996; 153: 321330.
  • 20
    Breier A, Schreiber JL, Dyer J et al. National Institute of Mental Health longitudinal study of chronic schizophrenia: Prognosis and predictors of outcome. Arch. Gen. Psychiatry 1991; 48: 239246.
  • 21
    Ho BC, Nopoulos P, Flaum M et al. Two-year outcome in first-episode schizophrenia: Predictive value of symptoms for quality of life. Am. J. Psychiatry 1998; 155: 11961201.
  • 22
    Meltzer HY, McGurk SR. The effects of clozapine, risperidone, and olanzapine on cognitive function in schizophrenia. Schizophr. Bull. 1999; 25: 233255.
  • 23
    Meltzer HY, Thompson PA, Lee MA et al. Neuropsychologic deficits in schizophrenia: Relation to social function and effect of antipsychotic drug treatment. Neuropsychopharmacology 1996; 14 (Suppl. 3): S27S33.
  • 24
    Velligan DI, Mahurin RK, Diamond PL et al. The functional significance of symptomatology and cognitive function in schizophrenia. Schizophr. Res. 1997; 25: 2131.
  • 25
    Heaton RK, Chelune GJ, Lehman RA. Using neuropsychological and personality tests to assess the likelihood of patient employment. J. Nerv. Ment. Dis. 1978; 166: 408416.
  • 26
    McGurk SR, Meltzer HY. The role of cognition in vocational functioning in schizophrenia. Schizophr. Res. 2000; 45: 175184.
  • 27
    Wilkinson G, Hesdon B, Wild D et al. Self-report quality of life measure for people with schizophrenia: The SQLS. Br. J. Psychiatry 2000; 177: 4246.
  • 28
    Kaneda Y, Fujii A, Ohmori T. Schizophrenia Quality of Life Scale: Validation of the Japanese version. Psychiatry Res. 2002; 113: 107113.
  • 29
    Heinrichs DW, Hanlon TE, Carpenter WT. The Quality of Life Scale: An instrument for rating the schizophrenic deficit syndrome. Schizophr. Bull. 1984; 10: 388398.
  • 30
    Heinrichs DW, Hanlon TE, Carpenter WT. The Quality of Life Scale. Seiwa Pub., Tokyo, 2001.
  • 31
    Kay SR, Fiszbein A, Opler LA. The positive and negative syndrome scale (PANSS) for schizophrenia. Schizophr. Bull. 1987; 13: 261276.
  • 32
    Bell MD, Lysaker PH, Beam-Goulet JL. Five-component model of schizophrenia: Assessing the factorial invariance of the positive and negative syndrome scale. Psychiatry Res. 1994; 52: 295303.
  • 33
    American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 4th edn. American Psychiatric Press, Washington, DC, 1994.
  • 34
    Inada T. Evaluation and Diagnosis of Drug–Induced Extrapyramidal Symptoms: Commentary on the DIEPSS and Guide to Its Usage. Seiwa Pub, Tokyo, 1996 (in Japanese).
  • 35
    Kaneda Y, Fujii A, Ohmori T. Psychometric properties of the Japanese version of the Calgary Depression Scale for Schizophrenics. J. Nerv. Ment. Dis. 2000; 188: 237239.
  • 36
    Inagaki A, Inada T. Dose equivalence of psychotropic drugs. Part 4. Dose equivalence of novel antipsychotics: Aripiprazole. Jpn. J. Clin. Psychopharmacol. 2006; 9: 249258 (in Japanese).
  • 37
    Ritsner M, Modai I, Endicott J. Differences in quality of life domains and psychopathologic and psychosocial factors in psychiatric patients. J. Clin. Psychiatry 2000; 61: 880889.
  • 38
    Bell MD, Lysaker PH, Milstein RM et al. Concurrent validity of the cognitive component of schizophrenia: Relationship of PANSS scores to neuropsychological assessments. Psychiatry Res. 1994; 54: 5158.
  • 39
    Hofer A, Rettenbacher MA, Widschwendter CG et al. Correlates of subjective and functional outcomes in outpatient clinic attendees with schizophrenia and schizoaffective disorder. Eur. Arch. Psychiatry Clin. Neurosci. 2006; 256: 246255.
  • 40
    Hofer A, Niedermayer B, Kemmler G et al. Cognitive impairment in schizophrenia: Clinical ratings are not a suitable alternative to neuropsychological testing. Schizophr. Res. 2006; 92: 126131.
  • 41
    Keefe RSE, Goldberg TE, Harvey PD et al. The Brief Assessment of Cognition in Schizophrenia: Reliability, sensitivity, and comparison with a standard neurocognitive battery. Schizophr. Res. 2004; 68: 283297.
  • 42
    Karow A, Moritz S, Lambert M et al. PANSS syndromes and quality of life in schizophrenia. Psychopathology 2005; 38: 320326.
  • 43
    Taniguchi T, Sumitani S, Aono M et al. Effect of antipsychotic replacement with quetiapine on the symptoms and quality of life of schizophrenic patients with extrapyramidal symptoms. Hum. Psychopharmacol. 2006; 21: 439445.
  • 44
    Jones PB, Barnes TR, Davies L et al. Randomized controlled trial of the effect on Quality of Life of second- vs first-generation antipsychotic drugs in schizophrenia: Cost Utility of the Latest Antipsychotic Drugs in Schizophrenia Study (CUtLASS 1). Arch. Gen. Psychiatry 2006; 63: 10791087.